Inkjet printing of functional materials for optical and photonic applications

Inkjet printing, traditionally used in graphics, has been widely investigated as a valuable tool in the preparation of functional surfaces and devices. This review focuses on the use of inkjet printing technology for the manufacturing of different optical elements and photonic devices. The presented overview mainly surveys work done in the fabrication of micro-optical components such as microlenses, waveguides and integrated lasers; the manufacturing of large area light emitting diodes displays, liquid crystal displays and solar cells; as well as the preparation of liquid crystal and colloidal crystal based photonic devices working as lasers or optical sensors. Special emphasis is placed on reviewing the materials employed as well as in the relevance of inkjet in the manufacturing of the different devices showing in each of the revised technologies, main achievements, applications and challenges

Next-generation organic blend semiconductors for high performance solution-processable field Effect Transistors

Ambitions for transparent, lightweight, flexible and inexpensive electronic technologies that can be printed over large area substrates have driven substantial advances in the field of organic/printed electronics in recent years. Amongst the various technologies investigated, solution-processed, organic thin-film transistors (OTFTs) have received extraordinary attention, primarily due to the enormous potential for simple, cost-effective manufacturing. Two exciting research areas relevant to OTFT development that offer tremendous potential are those of the small molecule/polymer organic semiconducting blends and the science and engineering of molecular doping. However, the lack of organic semiconducting blends that surpass the benchmark charge carrier mobility of 10 cm2/Vs, and the numerous challenges associated with the practical utilisation of molecular doping, have prevented adaptation of OTFTs as a viable technology for application in the emerging sector of plastic electronics. The work in this thesis focuses on an organic semiconducting system for OTFTs that addresses these two points. The first part of this thesis describes the development of advanced organic semiconducting blends, the so-called 3rd generation (3G) blend systems. Specifically, a new blend based on the small-molecule C8-BTBT and the conjugated polymer C16DT-BT is introduced. A third component, the molecular p-dopant, C60F48, is then added to the blend system and it is found to have remarkably positive effects on OTFT performance. The ternary blend system is then combined with a solvent-mixing approach, resulting in devices with an exceptional hole mobility value exceeding 13 cm2/Vs. Through the use of complementary characterisation techniques, it is shown that key to this achievement is the unusual three-component material distribution, hinting at the existence of an unconventional doping mechanism. Furthermore, by considering alternative processing techniques, the maximum mobility of the resulting OTFTs is improved further to a value in excess of 23 cm2/Vs. The second part of the thesis focuses on the impact of p-doping in the ternary C8 BTBT:C16IDT BT:C60F48 blend on other important operating characteristics of the OTFTs. The intentional and simple to implement doping process is shown to improve key device parameters such as bias-stress stability, parasitic contact resistance, threshold voltage and the overall device-to-device parameter variation (i.e. narrowing of the parameter spread). Importantly, the inclusion of the dopant is not found to adversely affect the nature of the C8 BTBT crystal packing at the OTFT channel. The final part of this thesis describes the incorporation of 3G blend-based OTFTs into fully functional logic electronic circuits. Hybrid inverter circuits (i.e. NOT gates) are fabricated at low temperatures from solution-phase by combining the high hole mobility C8-BTBT:C16IDT-BT:C60F48 blend OTFTs as the p-channel device and a novel In2O3/ZnO heterojunction metal oxide semiconducting system as the n-channel transistor. The resulting complementary inverters exhibit excellent signal gain and high noise margins, making this hybrid circuitry a promising contender for application in the emerging field of printed microelectronics.Open Acces

Al-In-Sn-O thin-film transistors

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 indium tin oxide (AITO) was designed and thin films were deposited via sputtering. AITO thin films have an excellent amorphous phase stability up to 725 °C. The effect of using ultra-thin channel layers was investigated. The turn-on voltage V[subscript ON] tends to strongly increase below a channel thickness of ~12 nm, allowing for the realization of enhancement-mode TFTs. Enhancement-mode TFTs with a channel thickness of 5-10 nm and a mobility of µ[subscript FE] = 15 - 18 cm²V⁻¹s⁻¹, drain current on-to-off ratio of I[superscript ON/OFF][subscript D] = 10⁷, and a sub-threshold swing of S = 0.2 V/dec were achieved

Investigation of structural properties of organic thin films for solar cell and transistor applications

For the past several decades, organic materials including polymers, oligomers and small molecules have been of great interest for their various applications in the electronics and the semiconductor industry. The most appealing advantages of organic materials compared to their inorganic counterparts are their compatibility with flexible substrates and amenability to low-temperature and low-cost fabrication processes such as evaporation, spin-coating and printing. Moreover, the ability to be utilized in fabrication of lightweight and large-area devices is among other reasons for popularity of organic materials. A large number of studies have reported on various aspects of the development and optimization of organic electronics such as organic light emitting diodes (OLEDs), solar cells (OSCs) and thin film transistors (OTFTs). Although significant progress has been made during this period, some of the intrinsic electrical properties of organic materials such as low carrier mobility have continued to hinder the full development and maturation of the organic electronics industry. In order to manufacture organic electronic devices with high performance, more detailed studies of the structure and the morphology of the organic materials as well as the underlying physical charge transport mechanisms should be performed. Additionally, growth, deposition and assembly processes need to be established and optimized for the new organic semiconductor technology.;This work aims to advance the understanding of the effect of the structural properties of organic thin films on the charge carrier transport within the organic thin films as well as the charge carrier injection between the organic layers and the organic-inorganic materials such as metal or dielectric layers. Charge carrier transport mechanisms between different layers are crucial factors in determining the efficiency of organic electronic devices. These parameters rely largely on the molecular structure, morphology and ordering of the organic thin films. In order to investigate these intrinsic properties, several organic thin films were prepared using vacuum thermal evaporation method. Their morphology and structural properties were studied by the combination of various techniques including atomic force microscopy, X-ray reflectivity, spectroscopic ellipsometry and transmittance measurements. Based on the produced organic thin films, organic semiconductor devices such as OTFTs and OSCs were fabricated and their electrical and optical properties were characterized. Moreover, the effect of morphology and structure of the organic thin films on the organic device performance was studied. Ambipolar thin film transistors based on pentacene and PTCDI-C8 as the active layer and lithium fluoride (LiF) as the gate dielectric layer were fabricated and characterized. Conduction behaviors of these devices were modeled using Fowler-Nordheim (FN) tunneling theory. The results of this study suggest that the charge transport in OTFTs correlate not only with the organic semiconductor film structure, but also with the dielectric--semiconductor interfacial effects. Moreover, bilayer heterojunction OSCs based on CuPc/PTCDI-C8 as the donor/acceptor layers were fabricated and their electrical and optical properties were characterized. The effects of the active layers\u27 structures and morphologies as well as the buffer layers\u27 thickness variation on the device performance were studied. The results of this study emphasized the importance of the thin film structural properties on the device performance

Promocijas darbs

Elektroniskā versija nesatur pielikumusŠajā darbā ir izklāstīti šķidro kristālu difuzoru projektēšanas un optimizācijas laikā iegūtie rezultāti, to ražošanas tehnoloģija un pielietojums uz galvas nēsājamos paplašinātās realitātes displejos. Šķidro kristālu difuzori tiek pielietoti liela izmēra displejiem, taču to pielietojums tuvu lietotāja acīm izvirza jaunas prasības attiecībā uz ļoti maziem izmēriem un augstu kontrastu, kā arī caurspīdīgumu. Piemērotas modelēšanas izmantošana šķidro kristālu sastāva projektēšanai un zināmo materiālu izmantošanas un tehnoloģijas optimizēšanai ļauj izpildīt augstāk minētās prasības ar samazinātu eksperimentālā darba apjomu. Gadījumos, kad tradicionālos displeju materiālus nevarēja izmantot, tika izstrādāti citi materiāli, proti, silīcija oksinitrīda plānās kārtiņas ar maināmu laušanas koeficientu.This thesis presents the results obtained during design and optimization of liquid crystal diffusers, their production technology and application in augmented reality head mounted displays. Liquid crystal diffusers have been proven for large form factor displays but their application for near eye distances provide new requirements in terms of very small dimensions, and high contrast and transparency. Using appropriate physical modelling to designing liquid crystal composition and for optimizing employment and technology of known materials, allows to fulfil above mentioned requirements with reduced volume of experimental work. In cases when traditional display technology materials could not be applied, other materials were developed, namely silicon oxy nitride thin films with variable index of refraction

Flat Panel Displays in Perspective

This report addresses two issues. First, is the lack of a high-volume domestic FPD industry a cause for national concern? Why might having such an industry be important for the good of the nation? Second, if the government wishes to foster such an industry, what policies might be most effective

Potential and recycling strategies for LCD panels from WEEE

Indium is one of the strategically important materials, which have been characterized as critical by various industrialized countries. Despite its high relevance, only low recycling rates are realized. Its main application is in indium tin oxide (ITO), which is used in the production of liquid crystal displays (LCD). However, recovery strategies for indium from LCDs are not yet being implemented in recycling practices. Although LCDs consist of a sandwich compound with additional materials such as glass (80% ± 5%) and polarizer foils (20% ± 5%), recently published recycling approaches focus mainly on the recovery of indium exclusively. This study, first of all, provides information about the quantity and quality of the materials applied in the LCD panels of the various equipment types investigated, such as notebooks, tablets, mobile phones, smartphones, PC monitors, and LCD TVs. The highest indium mass fraction per mass of LCD was determined in mobile phones and the least indium was found in smartphones. Additionally, we found the significant use of contaminating metals like antimony, arsenic, lead, and strontium in the glass fraction. Thus, specific recovery strategies should focus on selected equipment types with the highest indium potential, which is directly related to the sales of new devices and the number of collected end-of-life devices. Secondly, we have developed and successfully tested a novel recycling approach for separating the sandwich compound to provide single output fractions of panel glass, polarizer foils, and an indium concentrate for subsequent recycling. Unfortunately, the strongly varying content of contaminating metals jeopardizes the recycling of this output fraction. Nonetheless, economic recycling approaches need to address all materials contained, in particular those with the highest share in LCD panels such as polarizer foils and panel glass

アモルファスシリコン細線への大気圧マイクロ熱プラズマジェット照射による結晶成長制御とその高速CMOS回路作製への応用

広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora

Thin-Film Transistor Integration for Biomedical Imaging and AMOLED Displays

Thin film transistor (TFT) backplanes are being continuously researched for new applications such as active-matrix organic light emitting diode (AMOLED) displays, sensors, and x-ray imagers. However, the circuits implemented in presently available fabrication technologies including poly silicon (poly-Si), hydrogenated amorphous silicon (a-Si:H), and organic semiconductor, are prone to spatial and/or temporal non-uniformities. While current-programmed active matrix (AM) can tolerate mismatches and non-uniformity caused by aging, the long settling time is a significant limitation. Consequently, acceleration schemes are needed and are proposed to reduce the settling time to 20 µs. This technique is used in the development of a pixel circuit and system for biomedical imager and sensor. Here, a metal-insulator-semiconductor (MIS) capacitor is adopted for adjustment and boost of the circuit gain. Thus, the new pixel architecture supports multi-modality imaging for a wide range of applications with various input signal intensities. Also, for applications with lower current levels, a fast current-mode line driver is developed based on positive feedback which controls the effect of the parasitic capacitance. The measured settling time of a conventional current source is around 2 ms for a 100-nA input current and 200-pF parasitic capacitance whereas it is less than 4 μs for the driver presented here. For displays needed in mobile devices such as cell phones and DVD players, another new driving scheme is devised that provides for a high temporal stability, low-power consumption, high tolerance of temperature variations, and high resolution. The performance of the new driving scheme is demonstrated in a 9-inch fabricated display intended for DVD players. Also, a multi-modal imager pixel circuit is developed using this technique to provide for gain-adjustment capability. Here, the readout operation is not destructive, enabling the use of low-cost readout circuitry and noise reduction techniques. In addition, a highly stable and reliable driving scheme, based on step calibration is introduced for high precision displays and imagers. This scheme takes advantage of the slow aging of the electronics in the backplane to simplify the drive electronics. The other attractive features of this newly developed driving scheme are its simplicity, low-power consumption, and fast programming critical for implementation of large-area and high-resolution active matrix arrays for high precision

Direct printing of single-crystal silicon by microscale nanoparticle printing and confined laser melting and crystallization

The transport and interfacial phenomena in laser melting and crystallization of silicon in micro-/nano-scale confinement lacks sufficient understanding. Uncovering the underlying mechanisms, and hence harness the melting and crystallization processes can help the formation of controllable single-crystal structures or patterns. In this dissertation, a molecular dynamics (MD) simulation was conducted to calculate the interfacial free energy of the silicon system in contact with flat and structured walls. Then the calculated interfacial energies were employed to predict the nucleation mechanisms in a slab of liquid silicon confined by two walls and compared with MD simulation results. Further, in combination with a macroscopic model, it was concluded that for a given domain size, longer laser pulse increases the probability of forming single crystals. It was also suggested that for micro size Si domains, a continuous wave (CW) laser operated in a scanning mode can possibly generate single crystal structure. To examine the theoretical predication, CW laser crystallization of Si nanoparticles was conducted. A non-vacuum printing process, aerosol printing, was adopted in this dissertation, which enabled us to prepare Si film and lines with a cost-effective manner. Followed with pressing, the Si nanoparticles were densified and planarized. Then, the nanoparticles were laser melted and crystallized in the confined domain. It was found that the morphology and crystalline structure can be modulated from poly-crystal line to single-crystal islands through tuning the gap of confinement --Abstract, page iv