Solid solutions based on the perovskite ferroelectrics Bi₀.₅Na₀.₅TiO₃ (BNT) and Bi₀.₅K₀.₅TiO₃ (BKT) might someday replace current Pb-based ferroelectric and piezoelectric devices. This is one goal of the Restrictions on Hazardous Substances (RoHS) guidelines seeking to limit Pb in consumer devices. Although the Bi-based ferroelectrics are well suited to the task...
Magnetic thin films have potential to improve devices such as on-chip inductors, and enable new technologies such as magnetic random access memory (MRAM).
The use of magnetic cores in on-chip inductors is typically limited to applications well under 1 GHz. At higher frequencies, the performance of the magnetic core is...
Exciton polaritons are quasiparticles composed of a quantum superposition of matter and light states that arises from the coupling of a standing wave photon and an exciton. This research has two primary objectives: to design and fabricate a Fabry-Perot microcavity system in which to produce exciton polaritons; and to show...
The amorphous to crystalline phase change is of great interest for the production and operation of phase change memory and germanium electronic devices. Phase change memory relies on the ability to differentiate between differences in optical or electrical properties between the amorphous and crystalline phases of a single material. Amorphous...
In this dissertation, the structure and electronic properties of multiple metal oxide thin films are characterized and presented. Prompt inorganic condensation (PIC) of metal-oxo and –hydroxo clusters was evaluated as a technique for making metal oxide clusters in two separate studies. The first focuses on the synthesis of lithium niobate...
The growth of YMn₀.₃₅In₀.₆₅O₃ thin films and their optical and magnetic behavior are reported. The YMn₀.₃₅In₀.₆₅O₃ thin film grows along the (0001) orientation with hexagonal structure similar to YMnO₃ on c-plane sapphire. The film shows paramagnetic behavior in the temperature range measured. The film exhibits a blue color due to...
The optical transition in high-fraction polymorphs of titania (TiO2) were investigated to determine the band gap behavior of the most common polymorphs—brookite, rutile, and anatase—the values of which are varied in the literature. The direct optical band gaps of brookite, rutile, and anatase, were determined to be 3.37(7)eV, 3.41(11)eV and...
Zinc Sulfide (ZnS) thin film, with a wide band gap, has been used for many applications, such as buffer layer for CIGS solar cells, light emitting diodes and thin film electroluminescent devices.
In this work, ZnS thin films were prepared using two different deposition processes. In the first method, ZnS...
The focus of this thesis is developing materials for thin-film transistors (TFTs). Cu₃SbS₄ is explored as p-channel layer. Cu₃SbS₄ TFTs show p-type, depletion-mode behavior with a small amount of gate-controlled modulation of the channel conductance. This behavior is consistent with Hall measurements indicating a mobility of 17 cm²V⁻¹s⁻¹ and hole...
Copper sulfides (Cu[subscript x]S) are compound semiconductor materials that exhibit considerable optical and electrical properties varying significantly as a function of the composition. Copper sulfide thin films can be used in many applications, such as solar control coatings, solar cells, photothermal conversion of solar energy, electroconductive coatings, and microwave shielding...
Solid-state amorphous materials show amazing promise in thin-film electronics. The interface-to-bulk ratio of thin films makes interfacial chemistries of these systems of utmost importance. Thin films of amorphous metals, dielectrics and semiconductors have novel chemistries that are not only based upon their elemental constituent makeup, but also based upon the...
Researchers around the world use various solution-based deposition techniques to deposit thin films with multiple layers that typically require multiple rounds of deposition. Some such techniques include successive ionic layer adsorption and reaction (SILAR), and layer-by-layer (LBL) deposition.
One of the main issues with deposition of these types of films...
Pb(Zr,Ti)O₃ (PZT) is a very attractive material for use in piezoelectric-based microelectromechanical systems (MEMS) due to its high piezoelectric coefficients and ability for large displacements with relatively low applied fields (as compared to electrostatic-based MEMS). The piezoelectric effect is strongly anisotropic, thus it is very desirable to control the crystallographic...
The objective of the research presented herein is to elucidate the effect of traps in determining amorphous oxide semiconductor thin-film transistor (AOS TFT) performance using modeling and characterization. A novel method is proposed to extract the interface state distribution from a TFT transfer curve. Analysis of zinc-indium oxide (ZIO), zinc-tin...
The primary focus of this thesis is modifying the comprehensive depletion-mode model and extending its applicability to p-channel thin-film transistor (TFT) behavior and subthreshold (subpinchoff) operation. The comprehensive depletion-mode model accurately describes depletion-mode TFT behavior and establishes a set of equations, different from those obtained from square-law theory, which can...
Thin films are an enabling technology for a wide range of applications, from microprocessors to diffusion barriers. Nanolaminate thin films combine two (or more) materials in a layered structure to achieve performance that neither film could provide on its own. Atomic layer deposition (ALD) is a chemical vapor deposition technique...
Crystals of an incongruent-melting compound, Ba₃MgSi₂O₈, were grown by the flux method and its structure was determined by single crystal X-ray diffraction methods. Ba₃MgSi₂O₈ crystallizes in trigonal space group P-3[bar]m1 with a = 5.6123(3) Å, c = 7.2667(9) Å and Z = 1. Eu²⁺ ions prefer one crystallographic Ba site...
Metal-Organic Frameworks (MOFs) are crystalline compounds formed from reacting a metal ion with an organic ligand. They represent a promising new avenue in materials science for gas separations and storage. Certain MOFs, in particular Mg-MOF-74, have shown a strong affinity for the capture of CO2. This project investigated a known...
Digital printing techniques offer several advantages in manufacturing electronics such as direct writing of materials, reduction of chemical waste, and scalability. In particular, printing can significantly simplify manufacturing processes by directly defining the channel area, the gate, and the source and drain contacts, allowing for lower costs and higher throughput...
The aim of the research undertaken for this thesis was to develop a new high-performance amorphous oxide semiconductor (AOS) for use as a channel layer in a thin-film transistor (TFT). AOS TFTs offer higher electron mobility than the established amorphous silicon based technology. A new channel material comprised of aluminum...
Advances in energy technologies and electronics have typically occurred through either heightened performance or cost reduction. This dissertation explores both routes through a series of fundamental material studies that may contribute to the enabling of next generation devices. Solution based syntheses and deposition of chemical products offer a low cost...
The atomic solid state energy (SSE) scale is introduced as a tool for inorganic materials design. The SSE scale is obtained by assessing an average electron affinity (EA) (for a cation) or an average ionization potential (IP) (for an anion) for each atom using data from compounds having that specific...
BiCuOSe and SnS are layered, moderate band gap (ε[subscript G] ≈ 1 eV) semiconductors that exhibit intrinsic p type conductivity. Doping of BiCuOSe with Ca results in a slight expansion of the lattice and an increase of the hole concentration from 10¹⁸ cm⁻³ to greater than 10²⁰ cm⁻³. The large...
The central focus of this thesis is the design, fabrication and characterization of amorphous oxide semiconductor (AOS) thin-film transistor (TFT) current mirrors. The thin-film deposition and circuit fabrication methods used to realize zinc tin oxide (ZTO) TFT
current mirrors are addressed in order to elucidate the processing challenges for this...
This dissertation outlines two approaches for improving the efficiency and reducing the cost of photovoltaic energy generation. First, the structures of known binary copper and iron compounds are used to choose the promising compositions Fe₂XS₄ (X = Si, Ge), Cu₃TaQ₄ (Q = Se, Te), and BaCuQ'F (Q' = S, Se,...
Investigations on the application of self-assembled monolayers (SAM) to indium gallium zinc oxide (IGZO) thin film transistors (TFT) for fabrication and channel modification are presented. The back channel of IGZO thin film transistors can be modified by the absorption of self-assembled monolayers. The electrical properties of the IGZO exposed back...
Inkjet-printed p-type copper(I) iodide-based TFTs were successfully fabricated. As-printed copper(I) halide semiconductor films, such as CuI, CuBrI, and CuClI, were used as p-type active channel layers for TFTs. The entire process of the TFTs fabrication was maintained under 150 °C, which is compatible with flexible plastic substrates and transparent glass...
Nanostructured ZnO films were obtained via thermal oxidation of thin films formed with metallic Zn-nanoparticle dispersions. Commercial zinc nanoparticles used for this work were characterized by microscopic and thermal analysis methods to analyze the Zn-ZnO core shell structure, surface morphology and oxidation characteristics. These dispersions were spin-coated on SiO₂/Si substrates...
Thin-film transistors (TFTs) are primarily used as a switching element in liquid crystal
displays. Currently, amorphous silicon is the dominant TFT technology for displays, but
higher performance TFTs will become necessary to enable ultra-definition resolution
high-frequency large-area displays. Amorphous zinc tin oxide (ZTO) TFTs were
fabricated by RF magnetron sputter...
The research presented herein represents an effort to combine the ultra-smooth surface of an amorphous metal thin film (AMTF) with a solution-processed dielectric synthesized via prompt inorganic condensation (PIC). Analysis of dielectric film quality is carried out via electrical measurements of metal-insulator-metal (MIM) diodes. Anneals at 500 and 700 °C...
Microscale continuous thin films or patterned conductive structures find applications in thin film electronics, energy generation and functional sensor systems. An emerging alternative to conventional vacuum based deposition of such structures is the additive deposition and sintering of conductive nanoparticles, to enable low temperature, low- cost and low energy fabrication....
Polylactic acid (PLA), a renewable material, is used widely in a variety of commercial and specialty applications. However, certain limitations such as high temperature stability and brittleness limit its applicability. This problem is addressed by reinforcing PLA with a variety of materials but the process gives rise to different issues...
The objective of the work reported herein is to explore the impact of decreasing channel thickness on radio-frequency (RF) sputtered amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) electrical performance through the evaluation of drain current versus gate voltage (I[subscript D] − V[subscript G]) transfer curves. For a fixed set of...
Current cadmium telluride and copper indium gallium diselenide thin-film solar cells
(TFSCs) utilize thick absorbers (2 - 4 μm). For efficient carrier extraction in these TFSCs,
the absorber layer requires high carrier mobilities and a long minority carrier lifetime, which
necessitates the use of a high purity, defect-free thin film....
A scalable synthesis of the "flat" tridecameric inorganic cluster [Al₁₃(μ₃-OH)₆(μ-OH)₁₈(H₂O)₂₄]¹⁵⁺ has been realized by treating an aqueous aluminum nitrate solution with zinc-metal powder at room temperature. Single crystals and polycrystalline samples are readily obtained in yields exceeding 55% relative to the starting reagent Al(NO₃)₃. Products have been characterized by X-ray...
Piezoelectric materials have been widely used in electromechanical actuators, sensors, and ultrasonic transducers. Among these materials, lead zirconate titanate Pb(Zr[subscript 1‐x]Ti[subscript x])O₃ (PZT) has been primarily investigated due to its excellent piezoelectric properties. However, environmental concerns due to the toxicity of PbO have led to investigations into alternative materials systems....
Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs,...
The continuous microreactor-assisted solution deposition (MASD) process was used for the deposition of CdS thin films on fluorine-doped tin oxide (FTO) glass. The MASD system, including a T-junction micromixer and a microchannel heat exchanger is capable of isolating the homogeneous particle precipitation from the heterogeneous surface reaction. The results show...
Nanolaminate dielectrics combine two or more insulating materials in a many-layered film. These structures can be made to significantly outperform films composed of a single one of their constituent materials by adjusting the composition ratio, arrangement, and size of the component layers. In this work, atomic layer deposition (ALD) is...
Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) constitute the central theme of this thesis. Within this theme, three primary areas of focus are pursued.
The first focus is the realization of a transparent three-stage ring oscillator with buffered output and an output frequency in the megahertz range. This leads to...
As a group of promising semiconductor materials, metal chalcogenides in thin film form have been widely used in electronics and optoelectronics applications, such as solar cell devices and photon sensors. Unfortunately, the film size and product throughput are limited by the current vacuum-based thin film deposition techniques. Solution-based thin film...
Piezoelectric materials convert mechanical strain into a dielectric displacement, as well as the converse, allowing these materials to be used as sensors, actuators, and transducers. Currently, lead zirconate titanate (PZT) is the primary material used in these applications. Due to environmental toxicity and safety concerns associated with Pb, development of...
Nanomaterials are expected to enable significant advances in several technological fields in coming years. Among them, electronics has emerged as one of the most likely benefactors from the ability to control matter on the nanometer-scale. For many electronic devices synthesized nanomaterials must be integrated into thin film structures. Vapor-based deposition...
The development of solution-based methods for deposition of different thin film material is presented as an alternative to high cost vacuum-based methods. For certain materials, vacuum techniques are unsuitable for processing. Additionally, vacuum-based processes present high capital costs associated with equipment, and slow processing times. Atmospheric pressure solution based techniques...
Metal oxide nanocrystals have attracted significant interests due to their unique chemical, physical, and electrical properties which depend on their size and structure. In this study, a continuous flow microreactor system was employed to synthesize metal oxide nanocrystals in aqueous solution. Assembly of nanocrystals is considered one of the most...
Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT) thin films are of interest for their large dielectric permittivity, ferroelectric, and piezoelectric properties. The material has been widely studied for use in high frequency transducers, multi-layered capacitors, and ferroelectric random access memory. Copper foils are an inexpensive, flexible substrate with a low resistivity which makes them ideal...
Fabrication techniques and process integration considerations for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) constitute the central theme of this dissertation. Within this theme three primary areas of focus are pursued.
The first focus involves formulating a general framework for assessing passivation. Avoiding formation of an undesirable backside accumulation layer...
Cobalt germanides have been widely studied as semiconductor contact materials, but recent theoretical studies suggest that they may also be excellent catalysts for methane steam reforming with stabilities and activities comparable to noble metal catalysts. In order to study the catalytic activity of cobalt germanides, it is critical to first...
Transparent and electrically conductive metal oxide nanoparticles have attracted much attention, and can be used to improve the performance of solar cells, transparent electrode materials, and gas sensor technology. Specifically, indium tin oxide (ITO) nanocrystals (NCs) are potentially useful nanomaterials, having technological applications in enhanced sensitivity of optical spectroscopy due...
. ................................................................................................................... 7
Figure 3. Schematic illustration of the thinfilm gas sensor with ITO/MOF sandwich structure
To become a competitor for fossil fuels such as coal, solar installations will need to be produced and installed at a price equal to or below grid parity. This price can be approached by either reducing the overall system cost or increasing system efficiency. The focus of this paper is...