Review of Display Technologies Focusing on Power Consumption

Producción CientíficaThis paper provides an overview of the main manufacturing technologies of displays, focusing on those with low and ultra-low levels of power consumption, which make them suitable for current societal needs. Considering the typified value obtained from the manufacturer’s specifications, four technologies—Liquid Crystal Displays, electronic paper, Organic Light-Emitting Display and Electroluminescent Displays—were selected in a first iteration. For each of them, several features, including size and brightness, were assessed in order to ascertain possible proportional relationships with the rate of consumption. To normalize the comparison between different display types, relative units such as the surface power density and the display frontal intensity efficiency were proposed. Organic light-emitting display had the best results in terms of power density for small display sizes. For larger sizes, it performs less satisfactorily than Liquid Crystal Displays in terms of energy efficiency.Junta de Castilla y León (Programa de apoyo a proyectos de investigación-Ref. VA036U14)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA013A12-2)Ministerio de Economía, Industria y Competitividad (Grant DPI2014-56500-R

GaN Micro-LED Integration with Thin-Film Transistors for Flexible Displays

The research presented provides a systematic attempt to address the major challenges for the development of flexible micro-light-emitting diode (LED) displays. The feasibility of driving GaN-based micro-LEDs with a-Si:H-based thin-film transistors by using a thin-film bonding and transfer process was initially proposed. This approach was implemented to create an inverted pixel structure where the cathode of the LED is connected directly to the drain contact of the drive TFT resulting in a pixel circuit having more than 2× higher brightness compared to a standard pixel design. This “paste-and-cut” technique was further demonstrated for the development of flexible displays, enabling the study of the effect of mechanical strain and self-heating of the devices on plastic. Through a finite-element analysis, it was determined that the applied stress-induced strain near the quantum wells of the micro-LEDs are negligible for devices with diameters smaller than 20 microns. Thermal simulation of the LEDs on plastic revealed that a copper bond layer thicker than 600 nm can be used to alleviate self-heating effects of the micro-LEDs. Using these design parameters, micro-LED arrays with 20 micron diameter were integrated onto flexible substrates to validate the theoretical predictions. Further scaling of the LED size revealed substrate bending also tilts the direction of the LED structure, allowing further extraction of light. This effect was demonstrated using nanowire LEDs with a 250 nm diameter transferred onto plastic, where the light output could be enhanced by 2× through substrate bending. Finally, through the removal of bulk defect and surface states, fabrication of highly efficient micro-LEDs having > 400% increase in light output (compared to conventional diodes) was achieved. This outcome was accomplished through the removal of the defective buffer region adjacent to the active layers of the LED and minimization of the non-radiative recombination at the sidewalls. The former was accomplished through the removal of the buffer layer after separation of the LED from the process wafer while the latter is accomplished using a surround cathode gate electrode to deplete free carriers from the sidewall of the forward-biased LED. The resulting performance enhancements provided a basis for high-brightness flexible micro-LED displays developed in this dissertation

Organic Thin Film Transistor Integration

This thesis examines strategies to exploit existing materials and techniques to advance organic thin film transistor (OTFT) technology in device performance, device manufacture, and device integration. To enhance device performance, optimization of plasma enhanced chemical vapor deposited (PECVD) gate dielectric thin film and investigation of interface engineering methodologies are explored. To advance device manufacture, OTFT fabrication strategies are developed to enable organic circuit integration. Progress in device integration is achieved through demonstration of OTFT integration into functional circuits for applications such as active-matrix displays and radio frequency identification (RFID) tags. OTFT integration schemes featuring a tailored OTFT-compatible photolithography process and a hybrid photolithography-inkjet printing process are developed. They enable the fabrication of fully-patterned and fully-encapsulated OTFTs and circuits. Research on improving device performance of bottom-gate bottom-contact poly(3,3'''-dialkyl-quarter-thiophene) (PQT-12) OTFTs on PECVD silicon nitride (SiNx) gate dielectric leads to the following key conclusions: (a) increasing silicon content in SiNx gate dielectric leads to enhancement in field-effect mobility and on/off current ratio; (b) surface treatment of SiNx gate dielectric with a combination of O2 plasma and octyltrichlorosilane (OTS) self-assembled monolayer (SAM) delivers the best OTFT performance; (c) an optimal O2 plasma treatment duration exists for attaining highest field-effect mobility and is linked to a “turn-around” effect; and (d) surface treatment of the gold (Au) source/drain contacts by 1-octanethiol SAM limits mobility and should be omitted. There is a strong correlation between the electrical characteristics and the interfacial characteristics of OTFTs. In particular, the device mobility is influenced by the interplay of various interfacial mechanisms, including surface energy, surface roughness, and chemical composition. Finally, the collective knowledge from these investigations facilitates the integration of OTFTs into organic circuits, which is expected to contribute to the development of new generation of all-organic displays for communication devices and other pertinent applications. A major outcome of this work is that it provides an economical means for organic transistor and circuit integration, by enabling use of the well-established PECVD infrastructure, yet not compromising the performance of electronics

Chromium Modified Crystallization of Silicon Thin Films Crystallized by Flash Lamp Annealing

Flash lamp annealing (FLA) is a method of quickly crystallizing large areas of amorphous silicon, which is a promising alternative to existing low-throughput laser annealing in the fabrication of low temperature polycrystalline silicon for thin film transistors in display applications [1]. However, FLA tends to promote dewet- ting of silicon and randomized void formation during melt-phase crystallization [2]. Chromium underlayers have been successfully used [3] to promote silicon adhesion in thicker films, but there are many potential interactions between Cr and Si, such as the formation of silicides and generation of electrical trap states, that may inhibit future transistor performance. The mechanism and effects of these interactions are not yet understood. This work investigates the efficacy of chromium adhesion layers in silicon crystallization by FLA. Various thicknesses and configurations of amorphous silicon, thin chromium, and silicon dioxide barriers were deposited on glass and subjected to FLA. The resulting material was analyzed with electron and atomic-probe microscopy and found to contain a unique repeated pattern of voids, trenches, and SEM-bright spots at the nanometer scale. Energy-dispersive X-ray spectroscopy confirmed the distribution of chromium in crystallized films to be discrete Cr-rich agglomerations 50-70 nm in diameter, with little metallic contamination outside of these isolated areas

Characterization and Fabrication of Active Matrix Thin Film Transistors for an Addressable Microfluidic Electrowetting Channel Device

The characterization and fabrication of active matrix thin film transistors (TFTs) has been studied for an addressable microfluidic electrowetting channel device as application. A new transparent semiconductor material, Amorphous Indium Gallium Zinc Oxide (a-IGZO), is used for TFT, which shows high electrical performance rather than amorphous silicon based TFT; higher mobility and even higher transparency. The purpose of this dissertation is to optimize each TFT process including the optimization of a-IGZO properties to achieve robust device for application. To minimize hysteresis of TFT curves, the gate dielectric is discussed extensively in this dissertation. By optimizing gas ratio of NH3SiH4, it is found that the TFT with NH3 rich SiNx gate dielectric deposited with NH3/SiH4 =5.1 and stoichiometric SiO2 demonstrates best condition to reduce hysteresis. a-IGZO films is investigated as a function of power and substrate bias effect which affects to electrical performance; the higher power and substrate bias increase the carrier density in the film and mainly cause threshold voltage(VT) to shift in the negative gate voltage direction and mobility to increase, respectively. In addition, the powerful method to estimate the electrical properties of a-IGZO is proposed by calculating O2 and IGZO flux during sputtering in which the incorporation ratio with O2/IGZO ≈1 demonstrates the optimized a-IGZO film for TFT. It is confirmed that both physical and chemical adsorption affects the electrical property of a-IGZO channel by studying TFT-IV characteristics with different pressure and analyzing X-ray photoelectron spectroscopy (XPS), which mainly affects the VT instability. The sputtered SiO2 passivation shows better electrical performance. To achieve electrically compatible (lower back channel current) a-IGZO film to SiO2 sputter passivated device, a-IGZO TFTs require oxygen rich a-IGZO back channel by employing two step a-IGZO deposition process (2nd 10nm a-IGZO with PO2 = 1.5mTorr on 1st 40nm a-IGZO with PO2=1mTor). Electrowetting microfluidic channel device as application using a-IGZO TFTs is studied by doing preliminary test. The electrowetting channel test using polymer post device platform is candidate for addressable electrowetting microfluidic channel device driven by active matrix type a-IGZO TFT

The 2016 oxide electronic materials and oxide interfaces roadmap

Lorenz, M. et al.Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on ‘oxide electronic materials and oxide interfaces’. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action ‘towards oxide-based electronics’ which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.This work has been partially supported by the TO-BE COST action MP1308. J F acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (SEV-2015-0496) and MAT2014-56063-C2-1R, and from the Catalan Government (2014 SGR 734). F.M.G. acknowledges support from MIUR through the PRIN 2010 Project ‘OXIDE’.Peer reviewe

Options Under Uncertainty: An Empirical Investigation of Patterns of Commitment in Display Technologies in the Flat Panel TV Set Industry

This dissertation considers fundamental questions about real options reasoning and its application in the face of uncertainty: do firms behave as real options reasoning predicts, and are there performance benefits from its application? The concept of uncertainty is further developed by considering two primary types: technological uncertainty and market needs uncertainty. A qualitative industry level historical case study is performed on the flat panel TV industry, chosen because it exhibits high technological uncertainty and low market needs uncertainty. Real options logic predicts, in such an industry, that firms will develop and maintain technology options until uncertainty is resolved. Firm level case studies for major incumbent Japanese TV set manufacturers and other relevant firms are performed. Comparison across the cases, and between several specific firms is conducted to test and further develop theory. The firms studied are found to generally behave as predicted by real options logic. Evidence from the study does not present a clear relation between options-related behavior and performance. Although this study identifies evidence not holding options can have large negative performance results, firms holding options as predicted by theory did not realize lasting performance improvements. With one exception, firms attempting to leverage technological capabilities into improved market positions were unable to realize durable improvements in their positions. The development and release of flat panel TV coincided with changes in performance for many firms in the industry; however, these performance changes were short lived. By the end of the study period, industry players had generally returned to the trajectories they were previously on. Between-case analysis of several outlying firms in the sample provides a rich and nuanced view of requirements for firms to dramatically improve performance in the face of high technological uncertainty in a market with very large size potential and relatively well-understood customer needs. This research contributes to the empirical literature on real options and is novel amongst academic research in its coverage of the flat panel display history using Japanese sources. Finally, this dissertation includes managerial implications regarding the usefulness of real options reasoning as well as practical issues in its implementation

Toward Sustainable Transparent and Flexible Electronics with Amorphous Zinc Tin Oxide

The present thesis addresses a sustainable approach to mechanically flexible and transparent electronic devices based on the amorphous oxide semiconductor zinc tin oxide (ZTO) as abundant and low-cost alternative to already industrially established materials such as amorphous indium gallium zinc oxide. ZTO thin films are deposited by radio frequency long-throw magnetron sputtering at room temperature to generally enable the implementation of common photolithography processes and further facilitate patterning of digital circuit elements on thermally unstable organic substrates. Starting with the most basic device building blocks of integrated circuitry, various types of field-effect transistors are fabricated by implementation of amorphous ZTO as active channel material. Metal-semiconductor field-effect transistors and pn heterodiode based junctions field-effect transistors as well as conventional metal-insulatorsemiconductor field-effect transistors are then compared regarding their electrical performance and long-term stability over a couple of months. A decisive step toward the successful interconnection of fundamental digital circuit elements, such as previously demonstrated simple inverters, is to ensure sufficient output level compatibility between the signals of associated logic components. Accordingly, the Schottky diode field-effect transistor logic approach is adapted for amorphous ZTO based devices in order to facilitate cascading of multiple inverters consisting of unipolar devices. Field-effect transistor properties as well as the circuit design have been continuously improved to enhance the overall performance in terms of functionality and low-voltage operation. Corresponding logic inverters are finally integrated in ring oscillator circuits to gain insights into the dynamic properties of digital circuit building blocks based on amorphous ZTO. Ultimately, ZTO has been fabricated on mechanically flexible polyimide substrates to determine the elastic and electrical properties of amorphous ZTO thin films in dependence on external tensile and compressive stress induced by mechanical bending. Further, associated flexible metal-semiconductor field-effect transistor are investigated regarding their performance stability under tensile strain.Die vorliegende Arbeit umfasst die Herstellung und Charakterisierung aktiver elektrischer Bauelemente und integrierter Schaltkreise auf Basis des amorphen Oxidhalbleiters Zink-Zinnoxid (ZTO). Als vielversprechende nachhaltige und kostengünstigere Alternative zu dem bereits industriell etablierten Halbleiter Indium-Gallium-Zinkoxid wird insbesondere die Eignung von ZTO in optisch transparenter sowie mechanisch flexibler Elektronik untersucht. Um entsprechend Kompatibilität mit thermisch instabilen organischen Substraten sowie herkömmlichen Fotolithografieverfahren zu gewährleisten, beschränkt sich die Züchtung von ZTO-Dünnfilmen mittels Hochfrequenz-Magnetron-Distanzkathodenzerstäubung ausschließlich auf Herstellungsprozesse bei Raumtemperatur. Zunächst wird auf die Umsetzung verschiedener Feldeffekttransistor-Typen auf Basis amorphen ZTOs eingegangen, welche elektrisch charakterisiert und schließlich vor dem Hintergrund der Anwendung in integrierten Schaltkreisen vergleichend gegenübergestellt werden. Neben konventionellen Metall-Isolator-Halbleiterstrukturen wird vor allem näher auf Metall-Halbleiter-Feldeffekttransistoren sowie Sperrschicht-Feldeffekttransistoren auf der Grundlage von pn-Heteroübergängen eingegangen, da diese hauptsächlich in Bereichen hoher geforderter Schaltfrequenzen zum Einsatz kommen. Da integrierte Schaltkreise auf Basis unipolarer Feldeffekttransistoren eines Ladungsträgertyps inkonsistente Signaleingangs- sowie -ausgangspegel aufweisen, wird die Schottky- Dioden-Transistorlogik adaptiert, um entsprechend die Verknüpfung mehrerer Logikgatter auf Basis amorphen ZTOs zu gewährleisten. Durch geeignete Signalrückkopplung werden komplexere Schaltungen wie Ringoszillatoren realisiert, welche anhand von Laufzeitanalysen Aufschluss über die Schaltgeschwindigkeit ZTO basierter Feldeffekttransistoren geben. Abschließend werden amorphe ZTO-Dünnfilme auf flexiblen Polyimid-Substraten hergestellt und bezüglich der elastischen sowie elektrischen Eigenschaften in Abhängigkeit von exzessivem mechanischen Stress untersucht. Darüber hinaus werden flexible Metall-Halbleiter-Feldeffekttransistoren hinsichtlich ihrer Funktionalität und Stabilität gegenüber durch Biegeprozesse induzierte Verspannungen elektrisch charakterisiert