<p>Polymer nanocomposites are a constantly evolving material category due to the ability to engineer the mechanical, thermal, and optical properties to enhance the efficiency of a variety of systems. While a vast amount of research has focused on the physical phenomena of nanoparticles and their contribution to the improvement of such properties, the ability to implement these materials into existing commercial or newly emerging processing methods has been studied much less extensively. The primary characteristic that determines which processing technique is the most viable is the rheology or viscosity of the material. In this work, we investigate the processing methods and properties of nanocomposites for thermal interface and radiative cooling applications. The first polymer nanocomposite examined here is a two-component PDMS with graphene filler for 3D printing via a direct ink writing approach. The composite acts as a thermal interface material which can enhance cooling between a microprocessor and a heat sink by increasing the thermal conductivity of the gap. Direct ink writing requires a shear thinning ink with specific viscoelastic properties that allow for the material to yield through a nozzle as well as retain its shape without a mold following deposition. No predictive models of viscosity for nanocomposites exist; therefore, several prominent models from literature are fit with experimental data to describe the change in viscosity with the addition of filler for several different PDMS ratios. The result is an understanding of the relationship between the PDMS component ratio and graphene filler concentration with respect to viscosity, with the goal of remaining within the acceptable limits for printing via direct ink writing. The second nanocomposite system whose processability is determined is paint consisting of acrylic filled with reflective nanoparticles for radiative cooling paint applications. The paint is tested with both inkjet and screen-printing procedures with the goal of producing a thermally invisible ink. Radiative cooling paint is successfully printed for the first time with solvent modification. This work evaluates the processability of polymer nanocomposites through rheological tailoring. </p><br>

Ink-jet printing offers an ideal answer to the emerging trends and demands of depositing at ambient temperatures picoliter droplets of oxide solutions into functional thin films and device components with a high degree of pixel precision. It is a direct single-step mask-free patterning technique that enables multi-layer and 3D patterning. This method is fast, simple, easily scalable, precise, inexpensive and cost effective compared to any of other methods available for the realization of the promise of flexible, and/or stretchable electronics of the future on virtually any type of substrate. Because low temperatures are used and no aggressive chemicals are required for ink preparation, ink-jet technique is compatible with a very broad range of functional materials like polymers, proteins and even live cells, which can be used to fabricate inorganic/organic/bio hybrids, bio-sensors and lab-on-chip architectures. After a discussion of the essentials of ink-jet technology, this thesis focuses particularly on the art of designing long term stable inks for fabricating thin films and devices especially oxide functional components for electronics, solar energy conversion, opto-electronics and spintronics. We have investigated three classes of inks: nanoparticle suspension based, surface modified nanoparticles based, and direct precursor solution based. Examples of the films produced using these inks and their functional properties are: 1) In order to obtain magnetite nanoparticles with high magnetic moment and narrow size distribution in suspensions for medical diagnostics, we have developed a rapid mixing technique and produced nanoparticles with moments close to theoretical values (APL 2011 and Nanotechnology 2012). The suspensions produced have been tailored to be stable over a long period of time. 2)In order to design photonic band gaps, suspensions of spherical SiO2 particles were produced by chemical hydrolysis (JAP 2010 and JNP 2011 - not discussed in the thesis). 3) Using suspension inks, (ZnO)1-x(TiO2)x composite films have been printed and used to fabricate dye sensitized solar cells (JMR 2012). The thickness and the composition of the films can be easily tailored in the inkjet printing process. Consequently, the solar cell performance is optimized. We find that adding Ag nanoparticles improves the ‘metal-bridge’ between the TiO2 grains while maintaining the desired porous structure in the films. The photoluminescence spectra show that adding Ag reduces the emission intensity by a factor of two. This indicates that Ag atoms act as traps to capture electrons and inhibit recombination of electron-hole pairs, which is desirable for photo-voltaic applications. 4) To obtain and study room temperature contamination free ferromagnetic spintronic materials, defect induced and Fe doped MgO and ZnO were synthesized ‘in-situ’ by precursor solution technique (preprints). It is found that the origin of magnetism in these materials (APL 2012 and MRS 2012) is intrinsic and probably due to charge transfer hole doping. 5) ITO thin films were fabricated via inkjet printing directly from liquid precursors. The films are highly transparent (transparency &gt;90% both in the visible and IR range, which is rather unique as compared to any other film growth technique) and conductive (resistivity can be ~0.03 Ω•cm). The films have nano-porous structure, which is an added bonus from ink jetting that makes such films applicable for a broad range of applications. One example is in implantable biomedical components and lab-on-chip architectures where high transparency of the well conductive ITO electrodes makes them easily compatible with the use of quantum dots and fluorescent dyes. In summary, the inkjet patterning technique is incredibly versatile and applicable for a multitude of metal and oxide deposition and patterning. Especially in the case of using acetate solutions as inks (a method demonstrated for the first time by our group), the oxide films can be prepared ‘in-situ’ by direct patterning on the substrate without any prior synthesis stages, and the fabricated films are stoichiometric, uniform and smooth. This technique will most certainly continue to be a versatile tool in industrial manufacturing processes for material deposition in the future, as well as a unique fabrication tool for tailorable functional components and devices. / <p>QC 20120907</p>

The focus of this Ph.D. thesis research is a new piezoelectrically driven micromachined ultrasonic atomizer concept that utilizes fluid cavity resonances in the 15 MHz range along with acoustic wave focusing to generate the pressure gradient required for droplet or jet ejection. This ejection technique exhibits low-power operation while addressing the key challenges associated with other atomization technologies including production of sub-5 um diameter droplets, low-temperature operation, the capacity to scale throughput up or down, and simple, low-cost fabrication. This thesis research includes device development and fabrication as well as experimental characterization and theoretical modeling of the acoustics and fluid mechanics underlying device operation. The main goal is to gain an understanding of the fundamental physics of these processes in order to achieve optimal design and controlled operation of the atomizer. Simulations of the acoustic response of the system for various device geometries and different ejection fluid properties predict the resonant frequencies of the device and confirm that pressure field focusing occurs. High-spatial-resolution stroboscopic visualization of fluid ejection under various operating conditions is used to investigate whether the proposed atomizer is capable of operating in either the discrete-droplet or continuous-jet mode. The results of the visualization experiments combined with a scaling analysis provide a basic understanding of the physics governing the ejection process and allow for the establishment of simple scaling laws that prescribe the mode (e.g., discrete-droplet vs. continuous-jet) of ejection. In parallel, a detailed computational fluid dynamics (CFD) analysis of the fluid interface evolution and droplet formation and transport during the ejection process provides in-depth insight into the physics of the ejection process and determines the limits of validity of the scaling laws. These characterization efforts performed in concert with device development lead to the optimal device design. The unique advantages enabled by the developed micromachined ultrasonic atomizer are illustrated for challenging fluid atomization examples from a variety of applications ranging from fuel processing on small scales to ultra-soft electrospray ionization of biomolecules for bioanalytical mass spectrometry.

The objective of the research was to develop fundamental understanding of the process of deposition of complex mixtures by the inkjet method. The rheological properties and DOD drop formation dynamics of carbon black pigmented inkjet inks were investigated. It was found that the suspension microstructure responses to bulk motions, leading to shear rate and time dependent shear viscosity. However, DOD drop formation dynamics of highly pigmented inkjet ink and pure Newtonian fluid is similar even though shear rate up to 105 s-1 exists during inkjet jetting process. A proposed explanation for these observations is that the shearing time during DOD drop ejection is insufficient for changing and stabilizing the microstructure of the suspension. The effects of signal amplitude and jetting frequency on DOD drop formation dynamics of pure Newtonian fluids were investigated. A transition of DOD drop formation dynamics when the inkjet nozzle is switched from idle to jetting was identified. A qualitative investigation of DOD drop impaction and post-impaction behavior on inkjet paper and textiles was carried out. Dynamics of DOD drop accumulation and spreading on the substrates and final ink distribution show drastic differences between these two substrates.

This thesis investigates inkjet-printed flexible antennas fabricated on paper substrates as a system-level solution for ultra-low-cost and mass production of RF structures. These modules are designed for the UHF Radio Frequency Identification (RFID) Tags and Wireless Sensor Nodes (WSN); however the approach could be easily extended to other microwave and wireless applications. Chapter 1 serves as an introduction to RFID technology and its capabilities while listing the major challenges that could potentially hinder RFID practical implementation. Chapter 2 discusses the benefits of using paper as a substrate for high-frequency applications, reporting its very good electrical/dielectric performance up to at least 1 GHz. The dielectric properties are studied by using the microstrip ring resonator. Brief discussion on Liquid Crystal Polymer (LCP) is also given in this chapter. Chapter 3 gives details about the inkjet printing technology, including the characterization of the conductive ink, which consists of nano-silver-particles, while highlighting the importance of this technology as a fast and simple fabrication technique especially on flexible organic (e.g.LCP) or paper-based substrates. Chapter 4 focuses on antenna designs. Four examples are given to provide: i) matching techniques to complex IC impedance, ii) proof of concept of inkjet printing on paper substrate through measurement results, iii) demonstration of a fully-integrated wireless sensor modules on paper and show a 2D sensor integration with an RFID tag module on paper. Chapter 5 concludes the thesis by explaining the importance of this work in creating a first step towards an environmentally friendly generation of "green" RF electronics and modules.

This case study examined emitted sound and actuated piezoelectric current in a solderpaste jet printing machine to conclude whether quality degradation could be detected with an autoencoder machine learning model. An autoencoder was used to detect anomalies in non-realtime that were defined asa diameter drift with an averaging window from a target diameter. A sensor and datacollection system existed for the piezoelectric current, and a microphone was proposedas a new sensor to monitor the system. The sound was preprocessed with a Fast Fourier Transform to extract information of the existing frequencies. The results of the model, visualized through reconstruction error plots and an Area Under the Curve score, show that the autoencoder successfully detected conspicuous anomalies. The study indicated that anomalies can be detected prior to solder paste supply failure using the sound. When the temperature was varied or when the jetting head nozzle was clogged by residual solder paste, the sound model identified most anomalies although the current network showed better performance. / Denna fallstudie undersökte emitterat ljud och drivande piezoelektrisk ström i en jetprinter med lödpasta för att dra slutsatsen om kvalitetsbrister kunde detekteras med en autoencoder maskininlärningsmodell. En autoencoder användes för att detektera avvikelser definierade som diametertrend med ett glidande medelvärde från en bördiameter. Tidigare studier har visat att den piezoelektriska strömmen i liknande maskiner kan användas för att förutspå kvalitetsbrister. En mikrofon föreslogs som en ny sensor för att övervaka systemet. Ljudet förbehandlades genom en snabb fouriertransform och frekvensinnehållet användes som indata i modellen. Resultaten visualiserades genom rekonstruktionsfel och metoden Area Under the Curve. Modellen upptäckte framgångsrikt tydliga avvikelser. För vissa felfall visade ljudet som indata bättre prestanda än strömmen, och för andra visade strömmen bättre prestanda. Till exempel indikerade studien att avvikelser kan detekteras före lodpasta-försörjningsfel med ljudet. Under varierande temperatur och då munstycket var igentäppt av kvarvarande lödpasta identifierade nätverket med ljud som indata de flesta avvikelser även om nätverket med strömmen visade bättre prestanda.

<p>U disertaciji su predstavljena istraživanja uticajnih parametara<br />digitalne štampe na toplotna svojstva odjevnih predmeta, pri čemu su<br />kao parametri procesa štampe ispitani uticaji različitog broja<br />nanosa boje u štampi i različite tonske pokrivenosti. Odštampani<br />uzorci podvrgnuti su ispitivanjima toplotnih karakteristika<br />štampanih tekstilnih materijala. Na bazi analize izabranih<br />parametara razvijen je model toplotnih svojstava štampanih odjevnih<br />predmeta koji ima poseban značaj za predviđanje toplotno fiziološke<br />udobnosti odjeće tokom upotrebe.</p> / <p>У дисертацији су представљена истраживања утицајних параметара<br />дигиталне штампе на топлотна својства одјевних предмета, при чему су<br />као параметри процеса штампе испитани утицаји различитог броја<br />наноса боје у штампи и различите тонске покривености. Одштампани<br />узорци подвргнути су испитивањима топлотних карактеристика<br />штампаних текстилних материјала. На бази анализе изабраних<br />параметара развијен је модел топлотних својстава штампаних одјевних<br />предмета који има посебан значај за предвиђање топлотно физиолошке<br />удобности одјеће током употребе.</p>

The outstanding electrical and mechanical properties of single-walled carbon nanotubes (SWCNTs) may offer solutions to realizing high-mobility and high-bendability thin-film transistors (TFTs) for the emerging flexible electronics. This thesis aims to develop low-cost ink-jet printing techniques for high-performance TFTs based on pristine SWCNTs. The main challenge of this work is to suppress the effects of “metallic SWCNT contamination” and improve the device electrical performance. To this end, this thesis entails a balance between experiments and simulations.   First, TFTs with low-density SWCNTs in the channel region are fabricated by utilizing standard silicon technology. Their electrical performance is investigated in terms of throughput, transfer characteristics, dimensional scaling and dependence on electrode metals. The demonstrated insensitivity of electrical performance to the electrode metals lifts constrains on choosing metal inks for ink-jet printing.   Second, Monte Carlo models on the basis of percolation theory have been established, and high-efficiency algorithms have been proposed for investigations of large-size stick systems in order to facilitate studies of TFTs with channel length up to 1000 times that of the SWCNTs. The Monte Carlo simulations have led to fundamental understanding on stick percolation, including high-precision percolation threshold, universal finite-size scaling function, and dependence of critical conductivity exponents on assignment of component resistance. They have further generated understanding of practical issues regarding heterogeneous percolation systems and the doping effects in SWCNT TFTs.   Third, Monte Carlo simulations are conducted to explore new device structures for performance improvement of SWCNT TFTs. In particular, a novel device structure featuring composite SWCNT networks in the channel is predicted by the simulation and subsequently confirmed experimentally by another research group. Through Monte Carlo simulations, the compatibility of previously-proposed long-strip-channel SWCNT TFTs with ink-jet printing has also been demonstrated.   Finally, relatively sophisticated ink-jet printing techniques have been developed for SWCNT TFTs with long-strip channels. This research spans from SWCNT ink formulation to device design and fabrication. SWCNT TFTs are finally ink-jet printed on both silicon wafers and flexible Kapton substrates with fairly high electrical performance. / QC 20100910

Inkjet-printing is a technology which has for the last decade been exploited to fabricate flexible RF components such as antennas and planar circuit elements. However, the limitations of feature size and single layer fabrication prevented the demonstration of compact, and high efficiency RF components operating above 10 GHz into the mm-Wave regime which is critical to silicon integration and fully-printed modules. To overcome these limitations, a novel vertically-integrated fully inkjet-printed process has been developed and characterized up to the mm-Wave regime which incorporates up to five highly conductive metal layers, variable thickness dielectric layers ranging from 200 nm to 200 um, and low resistance through-layer via interconnects. This vertically-integrated inkjet printed electronics process, tagged VIPRE, is a first of its kind, and is utilized to demonstrate fully additive RF capacitors, inductors, antennas, and RF sensors operating up to 40 GHz. In this work, the first-ever fully inkjet printed multi-layer RF devices operating up to 40 GHz with high-performance are demonstrated, along with a demonstration of the processing techniques which have enabled the printing of multi-layer RF structures with multiple metal layers, and dielectric layers which are orders of magnitude thicker than previoulsy demonstrated inkjet-printed structures. The results of this work show the new possibilities in utilizing inkjet printing for the post-processing of high-efficiency RF inductors, capacitors, and antennas and antenna arrays on top of silicon to reduce chip area requirements, and for the production of entirely printed wireless modules.

This thesis investigates inkjet printing of fully-integrated modules fabricated on organic substrates as a system-level solution for ultra-low-cost and eco-friendly mass production of wireless sensor modules. Prototypes are designed and implemented in both traditional FR-4 substrate and organic substrate. The prototype on organic substrate is referred to as a Smart Wireless Integrated Module (SWIM). Parallels are drawn between FR-4 manufacturing and inkjet printing technology, and recommendations are discussed to enable the potential of inkjet printing technology. Finally, this thesis presents novel applications of SWIM technology in the area of wearable and implantable electronics. Chapter 1 serves as an introduction to inkjet printing technology on organic substrates, wireless sensor networks (WSNs), and the requirements for low-power consumption, low-cost, and eco-friendly technology. Chapter 2 discusses the design of SWIM and its implementation using traditional manufacturing techniques on FR-4 substrate. Chapter 3 presents a benchmark prototype of SWIM on paper substrate. Challenges in the manufacturing process are addressed, and solutions are proposed which suggest future areas of research in inkjet printing technology. Chapter 4 presents novel applications of SWIM technology in the areas of implantable and wearable electronics. Chapter 5 concludes the thesis by discussing the importance of this work in creating a bridge between current inkjet printing technology and its future.