To combat the effects of global warming, renewable energy sources are desirable but produce power intermittently, greatly limiting their ability to fulfill electricity demand on the grid. Storing energy produced for the grid and dispensing it at a later time would remove a major obstacle in the adoption of renewable energy sources. However, grid scale energy storage must be inexpensive to be cost-competitive with existing energy sources such as coal and natural gas. Batteries have been widely considered due to their energy storage capabilities, but existing technologies are too expensive, often limited by raw material cost and difficulty scaling to high capacity installations. Flow batteries are designed for scaling to high capacities, but existing materials remain too costly for widespread adoption.

Semi solid flow batteries (SSFB) are developed by forming suspensions of electrochemically active and conductive particles for use as an anolyte or catholyte in a flow battery. By utilizing micron-scale powders from mature battery chemistries in a flowable suspension, the benefits of energy-dense intercalation chemistries with the scalability of flow battery architectures can be combined for low cost electrochemical storage. Presently, a narrow set of materials has been explored, focusing on chemistries with a lithium anode. In this work, a magnesium SSFB with an optimized MoS2 cathodic slurry is demonstrated as a low cost and high material abundance alternative to lithium-based chemistries.

In this work, a mixed ionic-electronic conductive network is designed around a dual-ion (Mg2+, Li+) electrolyte, by combining the all-phenyl complex electrolyte (APC) with LiCl. MoS2 and Ketjenblack (KB) are dispersed in the APC+LiCl electrolyte to form the cathodic slurry. The rheological, electrical, and electrochemical properties of APC-MoS2-KB slurries with varying compositions have been measured. Full cells, with a Mg foil anode and MoS2 slurry cathode, are shown to cycle reversibly in a non-flowing and flowing configuration, reaching 225mAh/g discharge capacity. LiCl concentration and KB concentration are identified as critical to high capacity slurry cathodes. The relative impacts of Mg2+ and Li+ are quantitatively analyzed, showing that both ions are active and reversible during cycling. The rate capability of the optimized slurry is characterized and discussed, and long term cycling tests are presented, showing non-flowing and flowing slurry batteries for 135 cycles. This work provides experimental data and insight into how existing low cost material sets can be utilized in a semi solid flow battery architecture.

Printed batteries are an emerging battery technology that has the potential to enable the production of cheap, small form factor, flexible batteries capable of powering a diverse set of existing and emerging applications such as RFID tags, flexible displays, and distributed sensors. Partially printed battery systems have been demonstrated with various chemistries, but what is needed is a low cost, air stable method of fully printing a high energy density battery. The silver oxide chemistry is attractive for developing a printed battery as this chemistry has demonstrated high energy densities and is capable of air stable fabrication processes due to its aqueous based chemistry. To facilitate the advancement of this technology, material components and printing techniques need to be developed to demonstrate a printed silver oxide battery.

In this thesis, I will present a printed, high energy density silver oxide battery using stencil printing. A key development of this work is the demonstration of a novel photopolymerized polyacrylic acid separator layer. The mechanical and conductivity properties of this layer are characterized and optimized for an alkaline silver oxide battery. The incorporation of this layer has enabled a printed battery capable of high rates of discharge. The batteries show no difference in discharge upon flexing at a bend radius of 1.0 cm, indicating their potential in flexible applications. The fabricated batteries have demonstrated high energy densities of 10 mWhr cm ^-3 and areal capacities of 5.4 mAhr cm^-2, which satisfies the power and capacity requirements for most of the proposed applications. In addition, we have examined several printed encapsulation schemes (epoxy and silicone caulk) for encapsulating an alkaline battery.

Advances in research and technology are happening now more than ever in the biotechnology industry. Efficient methods for biological processes and better detection and treatment methods are constantly being sought by researchers. Collaboration among different fields of science and technology has brought us one step closer towards achieving this goal in this work. One such technology that has the capability of providing efficient methods and processes for biology is printed electronics. Printed electronics is an attractive paradigm for realization of biological microfluidic systems. The large area of these systems makes printing valuable from a cost perspective. Furthermore, since printing allows for easy integration of disparate materials on the same substrate through spatially-specific deposition, printed electronics is particularly useful for integration of diverse biological microfluidic functionality on the same substrate.

While there have been instances of printed transistors and passive components, there have been no demonstrations to date of the critical components required for biological microfluidic applications or lab on a chip (LOC) devices. In this work, for the first time, we present all-printed gold heaters, gold resistive temperature detectors, and electrostatically actuated PDMS microfluidic valves designed for biological microfluidic applications. In addition, work on DNA sensors using printable organic (pentacene) thin film transistors (OTFTs) is also presented for use in LOC devices.

Many biological applications require precise control and stability of temperature, which is demonstrated here through the integration of printed heaters and printed RTDs into a microchip bioprocessor system capable of polymerase chain reaction (PCR). Flow rate measurements and dynamic characteristics of printed PDMS valves are also presented to demonstrate the effectiveness of these devices. With the 440 microns wide and 16 microns deep microfluidic channels used in this project, the valve with the thinnest PDMS membrane (55 microns) closed the channel completely (i.e. flow rate = 0) at a pull-in voltage of 250V. This valve closed and opened in approximately 1.5 and 5.5 seconds, respectively. Pentacene surface has also been optimized to arrive at the best sensitivity for DNA immobilization and hybridization, bringing us a step closer in realizing printed OTFT DNA sensors for `tag-free' electrical detection. To summarize the sensor results, thinner films, higher substrate temperature, and higher input current during pentacene evaporation ensured that DNA immobilized in the channel part of the transistor and therefore provided for highest sensitivity of pentacene film to DNA.

This work has thus successfully revealed the potential of printed electronics in real-world biological applications and has also paved the way for exciting future research areas for this technology.

The field of low-cost and solution-processed electronics has experienced a steady increase in research interest over the past two decades. Fueled by continuous advances in materials development and deposition techniques, low-cost, printable electronics are approaching reality. However, a number of advances remain to be accomplished in order to enable some key, sought after applications, such as displays and RFID tags. In particular, to realize such systems, it will be necessary to facilitate the development of a number of underlying electronic devices, including conductors, transistors, and memory technologies. These particular devices are the focus of this work.

This work is focused on transparent thin film transistors (TFTs) and conductors for flexible displays and memories for printed RFID tags. TFTs and conductors are based on ink-jet printed reduced graphene oxide (rGO). Conditions for achieving good printed features, such as jetting dynamics, ink formulation, and printing temperature control are examined. Effects of these conditions, as well as various annealing schemes, on electrical performance are presented. Physical properties of printed films are investigated by atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS). Resulting devices exhibit drive currents up to 1 μA, current ON/OFF ratios of up to 10, and field effect mobilities of up to 0.018cm²/V-s. Presented drive currents and mobilities are sufficient to drive a basic display pixel; however, larger ON/OFF ratios are generally required. Potential solutions to achieving higher ON/OFF ratios, such as use of nano-ribbon graphene inks or dual gate structures, are proposed.

Memory presented in this work is based on filamentary switching in a silver/zinc oxide/gold (Ag/ZnO/Au) stack. There, diffusing Ag ions can reversibly form conducting paths through the ZnO electrolyte, thereby accomplishing data storage by changing the resistive state of the cell. A fully solution-processed cell is presented along with control cells based on evaporated metal contacts. Overall, good memory characteristics are observed: long retention time, cycling endurance of over 2000 cycles, good memory window, and minimum programming time of 200 ns. Filament growth dynamics are examined via potentiostatic, potentiodynamic, and temperature measurements. With the exception of a high temperature ZnO annealing step (350°C), these memories are fully-printable and plastic-compatible. Possible solutions for achieving low-temperature ZnO are presented, such as plasma treatments of deposited films and alternative sol-gel deposition techniques. With the incorporation of plastic-compatible electrolyte, this memory technology presents a promising candidate for printed electronics.

Electronic noses have been studied for decades, but are still relatively uncommon in commercial use because fabricating a gas sensor array, the heart of the electronic nose, is costly and difficult. Commonly, the most difficult part of fabricating a sensor array is integrating the individual sensor elements into one platform, an expensive proposition using current gas sensors like metal oxide devices. Thin film transistors (TFTs) made from polythiophene, an organic semiconductor, stand to be attractive candidates for sensor arrays because they can be easily arrayed with deposition methods like inkjet printing and they have a rich chemistry that can exploited to tune their sensor behavior. The thesis of this work is that functionalized polythiophene TFTs are compelling, and perhaps superior, candidates in sensor arrays for electronic nose applications.

First, polythiophene TFTs are demonstrated to be viable gas sensors. Basic electrical and sensing behavior is introduced and initial metrics and difficulties are addressed. Physical characterizations of polythiophene based gas sensors are carried out using Grazing Incidence X-ray Diffraction (GIXD), X-ray Reflectivity (XRR), and Quartz Crystal Microbalance (QCM) techniques. Novel in situ XRR and QCM measurements have shown, for the first time, the presence of a physical interaction between the gaseous analyte and the sensor film. These physical changes are corroborated and compared with the electrical response. Strategies for engineering better gas sensors are proposed and demonstrated. Using elegant and robust motifs, simple but powerful sensor arrays are fabricated that demonstrate discrimination between analytes even in the presence of mixtures. These arrays are capable of discriminating analytes based on the size and arrangement of their molecules, an important but previously unexplored avenue. Discrimination based on the analyte's functional groups is also presented. Based on these findings, a mechanistic model is also proposed which is consistent with experimental observations and highlights more pathways for engineering better sensor arrays.

Intracortical recording devices have the capability to bring functionality back to people that have lost it through neurological conditions and injuries. These devices have been demonstrated in humans to control robotic limbs and enable brain-to-text communication. One major drawback of current intracortical recording technology is the limited effective recording lifetime of implant technology. To evaluate the lifetime of implants, durability studies are performed on implant designs. Current in vitro accelerated aging methods use heated saline baths intended to accelerate implant degradation using elevated temperatures and hydrogen peroxide to simulate the reactive oxygen attack that implants undergo as a part of the foreign body response. The focus of this thesis will be on the development of a microfluidic platform for durability evaluation of intracortical recording devices as well as a novel aging method that uses immune cells to simulate this reactive species attack. This work describes a microfluidic chamber design and fabrication process as well as techniques to control the reactive oxygen attack in the microreactor. The degradation of neural probes aged in microfluidic chambers using the saline/hydrogen peroxide method and the immune cell method is evaluated and compared to in vivo device degradation. An acceleration factor for immune cell aging is proposed for the acceleration of the reactive oxygen-induced polymer chain scission that occurs in vivo. Lastly, this work presents a model for implant lifetime prediction that incorporates both biological and material failure mechanisms using an equivalent circuit model for a neural implant.

In recent years, resistive random access memory (RRAM) has gained significant attention as one of the promising candidates for next generation memory applications. This is due to its anticipated advantages versus Flash technology with respect to high density, low power and fast read and write speed. The main operation mechanism of these devices is a resistance change induced by filament formation through metal-cations or oxygen vacancies.

In the first part of this work, a Kinetic Monte Carlo (KMC) simulator is built to study the filament formation process in an electrochemical metallization (ECM) RRAM. This simulator takes into account most important physical and chemical processes such as oxidation, reduction, metal crystallization, adsorption, desorption and ionic transportation. The characteristics of the forming voltage, forming time and switching speed are investigated. In addition, studies on filament overgrowth and on-state resistance distribution are presented. Further, filament topography, which strongly influences device properties, is studied under different device operation conditions. The simulator also predicts that depending on the strength of lateral electric field, the conductive filament can break at various locations during the RESET process. The simulation results are verified by experiments conducted on Ag/Ag2S/W and Cu/H2O/Cu systems.

In the second part of this work, RRAM memory devices based on amorphous Yttria stabilized Zirconia (YSZ) are systematically studied. The effects of different top electrodes of Au, Cu, Ni, Al and Ti are investigated. And the characteristics and the mechanisms of Ti/YSZ and Cu/YSZ are studied in details. It is found that Ti/YSZ has much better endurance, retention and reliability than Cu/YSZ. The underlining physics driving this behavior is investigated. In addition, it is found that Ti/YSZ has very smooth transition in the RESET stage and the off state resistance exponentially increases with an increase of erase voltage. Based on those properties, a multi-level programming (MLP) cell is realized that shows good endurance. The underlying physics that makes the MLP possible for Ti/YSZ is investigated. Finally, it is shown that an incremental step pulse programming (ISPP) technique can significantly increase the device endurance and reliability. Furthermore, it can optimize the tradeoff between resistance programming window and device lifetime.

Transparent electronics has been considered as a critical key to solve problems exhibited by virtually all flat panel displays and solar cells. Transparent electronics is expected to allow for the realization of displays with high aperture ratio for high brightness. This will enable the embedding of system-level electronics directly onto the display glass. The minimization of light lost when going through multi-layer stack structures is a major opportunity for solar cells and particularly for transparent solar cells consisting of transparent photovoltaic units. Over the last decade, amorphous phase and poly crystalline metal oxides, including ZnO, In2O3, and SnO2 and their ternary and quaternary alloys, have been considered as candidates for transparent electronics. Using conventional vacuum-based deposition techniques and lithography technology, metal oxide based transistors with field effect mobility values high enough for the simultaneous operation of integrated circuits, pixel drivers and peripheral drivers have been demonstrated. In addition, by combining transparent source, drain, and gate electrodes with a transparent insulator, fully transparent circuits can be fabricated. Normally, hetero- junction solar cells consist of an absorber layer, its metal contacts, window layers, and their metal contacts. Transparent metal oxide n-type conducting window layers can be fabricated with the aforementioned semiconductors (ZnO, In2O3 or SnO2). These layers provide a large band gap, excellent electronic transport properties, and easy metal contact formation. Among the aforementioned metal oxides SnO2 has its own promising characteristics. It has a larger band-gap, lower melting point and higher bulk mobility Thus, a high-quality SnO2 layer can potentially be created at a relatively low sintering temperature resulting in high performance transistor characteristics.

The main goals of this field are to improve process throughput for large area panels, to lower fabrication cost and to improve device performance. Combining the aforementioned attractive properties of SnO2 with the process benefits of inkjet printing, fully ink-jet printed SnO2 TFTs were demonstrated as a good candidate to achieve these main goals. To realize this, SnO2, ZrO2, and Sb-doped SnO2 were selected for the transparent semiconductor, the insulator and the electrodes respectively. Solution phase

sol-gel precursors were used as inks for inkjet printing to form these materials. To fabricate uniform and coffee ring less layers, the spreading speed and evaporation rate were controlled by addition of a high-viscosity solvent mixture and with increased substrate temperatures. Using these innovations, transparent metal-oxide-based transistors were fabricated on glass substrates. These devices consisted of a SnO2 semiconductor layer, a ZrO2 insulator layer and Sb-doped SnO2 electrodes formed through ink-jet printing. They exhibited excellent transistor characteristics, and thus represent a promising step towards making printed transparent electronic systems a reality.

Primarily used as transparent electrodes in solar-cells, more recently, physical vapor deposited

(PVD) transparent conductive oxide (TCO) materials (e.g. ZnO, In2O3 and SnO2)

also serve as the active layer in thin-film transistor (TFT) technology for modern liquidcrystal

displays. Relative to a-Si:H and organic TFTs, commercial TCO TFTs have reduced

off-state leakage and higher on-state currents. Additionally, since they are transparent, they

have the added potential to enable fully transparent TFTs which can potentially improve

the power efficiency of existing displays.

In addition to PVD, solution-processing is an alternative route to the production of displays

and other large-area electronics. The primary advantage of solution-processing is in

the ability to deposit materials at reduced-temperatures on lower-cost substrates (e.g. glass,

plastics, paper, metal foils) at high speeds and over large areas. The versatility offered by

solution-processing is unlike any conventional deposition process making it a highly attractive

emergent technology.

Unfortunately, the benefits of solution-processing are often overshadowed by a dramatic reduction

in material quality relative to films produced by conventional PVD methods. Consequently,

there is a need to develop methods that improve the electronic performance of

solution-processed materials. Ideally, this goal can be met while maintaining relatively low

processing temperatures so as to ensure compatibility with low-cost roll-compatible substrates.

Mobility is a commonly used metric for assessing the electronic performance of semiconductors

in terms of charge transport. It is commonly observed that TCO materials exhibit significantly

higher field-effect mobility when used in conjunction with high-k gate dielectrics (10

to 100 cm2 V−1

s

−1

) as opposed to conventional thermally-grown SiO2 (0.1 to 20 cm2 V−1

s

−1

).

Despite the large amount of empirical data documenting this bizarre effect, its physical ori-

2

gin is poorly understood.

In this work, the interaction between semiconductor TCO films and high-k dielectrics is

studied with the goal of developing a theory explaining the observed mobility enhancement.

Electrical investigation suggests that the mobility enhancement is due to an effective doping

of the TCO by the high-k dielectric, facilitated by donor-like defect states inadvertently

introduced into the dielectric during processing. The effect these states have on electron

transport in the TCO is assessed based on experimental data and electrostatic simulations

and is found to correlate with negative aspects of TFT behavior (e.g. frequency dispersion,

gate leakage, hysteresis, and poor bias stability).

Based on these findings, we demonstrate the use of an improved device structure, analogous

to the concept of modulation doping, which uses the high-k dielectric film as an encapsulate,

rather than a gate-dielectric, to achieve a similar doping effect. In doing so, the enhanced

mobility of the TCO/high-k interface is retained while simultaneously eliminating the negative

drawbacks associated with the presence of charged defects in the gate dielectrics (e.g.

frequency dispersion, gate leakage, hysteresis, and poor bias stability). This demonstrates

improved understanding of the role of solution-processed high-k dielectrics in field-effect

devices as well as provides a practical method to overcome the performance degradation

incurred through the use of low-temperature solution-processed TCOs.