A unified OLED aging model combining three modeling approaches for extending AMOLED lifetime

Aging is still the most challenging issue for organic light-emitting diodes (OLEDs), which causes the image-sticking artifacts on active-matrix organic light-emitting diode (AMOLED) displays and limits their lifetime. To overcome this demerit, an aging model is necessary to compensate for aging artifacts. In this paper, we present a unified OLED aging model, which combines three feasible modeling approaches of OLED degradation, namely, datacounting, electro-optical, and correlation methods. The model can be used to predict the efficiency decay of OLED pixels during operation. It mitigates weaknesses and limitations of each of these three models and deploys their strengths, respectively. In the first aging stage, the data-counting model is prioritized, and in the later stages, it is calibrated using the correlation model. The dependency of the efficiency decay on the operation point of OLED is covered by the electro-optical model. The unified model is based on both phenomenal and physical effects. It delivers more reliability to determine an OLED's degradation over a long-term operation and a wide operation range like current amplitude and/or temperature range. The unified aging model applies to either an analog or a digital driving scheme. A corresponding compensation based on the aging model can be applied for extending the AMOLED lifetime

The 2021 flexible and printed electronics roadmap

This roadmap includes the perspectives and visions of leading researchers in the key areas of flexible and printable electronics. The covered topics are broadly organized by the device technologies (sections 1–9), fabrication techniques (sections 10–12), and design and modeling approaches (sections 13 and 14) essential to the future development of new applications leveraging flexible electronics (FE). The interdisciplinary nature of this field involves everything from fundamental scientific discoveries to engineering challenges; from design and synthesis of new materials via novel device design to modelling and digital manufacturing of integrated systems. As such, this roadmap aims to serve as a resource on the current status and future challenges in the areas covered by the roadmap and to highlight the breadth and wide-ranging opportunities made available by FE technologies

Error-efficient computing systems

This survey explores the theory and practice of techniques to make computing systems faster or more energy-efficient by allowing them to make controlled errors. In the same way that systems which only use as much energy as necessary are referred to as being energy-efficient, you can think of the class of systems addressed by this survey as being error-efficient: They only prevent as many errors as they need to. The definition of what constitutes an error varies across the parts of a system. And the errors which are acceptable depend on the application at hand. In computing systems, making errors, when behaving correctly would be too expensive, can conserve resources. The resources conserved may be time: By making some errors, systems may be faster. The resource may also be energy: A system may use less power from its batteries or from the electrical grid by only avoiding certain errors while tolerating benign errors that are associated with reduced power consumption. The resource in question may be an even more abstract quantity such as consistency of ordering of the outputs of a system. This survey is for anyone interested in an end-to-end view of one set of techniques that address the theory and practice of making computing systems more efficient by trading errors for improved efficiency

High dynamic range display systems

High contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast response time, and is fail-safe. To reduce the weight and size of a display system, we proposed a functional reflective polarizer, which can also help people with color vision deficiency. As for the HDR display, we improved all three aspects of the hardware requirements: contrast ratio, color gamut and bit-depth. By stacking two liquid crystal display (LCD) panels together, we have achieved CR over one million to one, 14-bit depth with 5V operation voltage, and pixel-by-pixel local dimming. To widen color gamut, both photoluminescent and electroluminescent quantum dots (QDs) have been investigated. Our analysis shows that with QD approach, it is possible to achieve over 90% of the Rec. 2020 color gamut for a HDR display. Another goal of an HDR display is to achieve the 12-bit perceptual quantizer (PQ) curve covering from 0 to 10,000 nits. Our experimental results indicate that this is difficult with a single LCD panel because of the sluggish response time. To overcome this challenge, we proposed a method to drive the light emitting diode (LED) backlight and the LCD panel simultaneously. Besides relatively fast response time, this approach can also mitigate the imaging noise. Finally yet importantly, we improved the display pipeline by using a HDR gamut mapping approach to display HDR contents adaptively based on display specifications. A psychophysical experiment was conducted to determine the display requirements

OLEDs AND E-PAPER. Disruptive Potential for the European Display Industry

DG ENTR and JRC/IPTS of the European Commission have launched a series of studies to analyse prospects of success for European ICT industries with respect to emerging technologies. This report concerns display technologies (Organic Light Emitting Diodes and Electronic Paper - or OLEDs and e-paper for short). It assesses whether these technologies could be disruptive, and how well placed EU firms would be to take advantage of this disruption In general, displays are an increasingly important segment of the ICT sector. Since the 1990s and following the introduction of flat panel displays (FPDs), the global display industry has grown dramatically. The market is now (2009) worth about ¿ 100 billion. Geo-politically, the industry is dominated by Asian suppliers, with European companies relegated to a few vertical niches and parts of the value chain (e.g. research, supply of material and equipment). However, a number of new technologies are entering the market, e.g. OLEDs and electronic paper. Such emerging technologies may provide an opportunity for European enterprises to (re-)enter or strengthen their competitive position. OLEDs are composed of polymers that emit light when a current is passed through them. E-paper, on the other hand, is a portable, reusable storage and display medium, typically thin and flexible. Both OLEDs and e-paper have the potential to disrupt the existing displays market, but it is still too soon to say with certainty whether this will occur and when. Success for OLEDs depends on two key technical advances: first, the operating lifetime, and second, the production process. E-paper has a highly disruptive potential since it opens the door to new applications, largely text-based, not just in ICTs but also in consumer goods, pictures and advertising that could use its key properties. It could also displace display technologies that offer text-reading functions in ICT terminals such as tablet notebooks. There are three discrete segments in the OLED value chain where any discontinuity could offer EU firms the opportunity to play a more significant part in the displays sector: (1) original R&D and IPR for devices and for the manufacturing process and material supply/verification; (2) bulk materials for manufacture and glass; and (3) process equipment:. For the e-paper value chain, we can see that the entry of EU suppliers is perhaps possible across more value chain segments than for OLEDs. Apart from the ones mentioned for OLEDs, there are opportunities to enter into complete devices and content provision. In terms of vertical segments, the point of entry in OLED FPDs for Europe is most likely to be in the mass production of smaller FPDs for mobile handsets. In conclusion, OLEDs and e-paper have the potential to disrupt current displays market and in so doing they may enable EU companies to enter at selected points in the value chain to compete with the Asian ICT industry.JRC.J.4-Information Societ

유기 발광 소자에 대한 임피던스 분광 분석 방법에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2019. 2. 홍용택.In this dissertation, the method of analyzing the characteristics of organic light-emitting diodes using impedance spectroscopy was studied. Generally, the organic light-emitting device has a structure in which organic materials necessary for light emission are thinly laminated between a TCO (Transparent Conductive Oxide) and a metal electrode. Due to chemical vulnerability of organic materials as well as the complexity with their hetero-junction, it is necessary to investigate the characteristics of fabricated an organic light-emitting diodes in a non-destructive manner rather than destructive manner. Classically, a method of measuring a current-voltage curve using a current-voltage meter and measuring a luminescence using luminance meter is used to evaluate the characteristics of the OLEDs. However, in order to investigate details at intrinsic interface state or carrier dynamics of OLEDs, it is require measuring the impedance response under operating condition. Impedance spectroscopy (IS) covers all impedance responses in the frequency range from milli hertz to megahertz, while focusing primarily on capacitance in solid-state electronics. This makes it possible to construct a high-resolution equivalent circuit and analyze each measured impedance. Each impedance is measured by applying ac small signal after determining the dc operating voltage. The dc operating voltage and ac small signal should be strategically chosen to describe the behavior of the device. In Chapter 1, an overview of the Impedance Spectroscopy Analysis is introduced and the background of the impedance measurement method is explained. Then the motivation for applying this impedance analysis method to OLEDs is explained and the methods of analyzing the characteristics of OLEDs through impedance spectroscopy are discussed. Chapter 2 reviews previously reported papers about impedance analysis methods of OLEDs and explains the limitations of these papers. In particular, the contributions of the diffusion capacitance that they underestimate are very important to prevent errors when characterizing of OLEDs. To explained diffusion capacitance the Laux & Hess model is applied. This model can explain the impedance response to the residual current and even demonstrate the negative capacitance phenomenon. The analytical results using the Laux & Hess model[1] were verified to describe the characteristics of the OLEDs during operation and an approximate and fitting process for the analytical method of this model is proposed. In Chapter 3, ITO/a-NPD[N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-2,2′-dimethylbenzidine]/Alq3[Tris-(8-hydroxyquinolinato)aluminum]/LiF/Al type OLEDs were fabricated and investigated using the improved impedance analysis method proposed in Chapter 2. First, according to the structural (thickness) change, the physical analysis was performed quantitatively by changing the impedance response. The measured impedance at high frequencies represents the interface and buck characteristics in the OLEDs, and the impedance at low frequencies explains the dynamics of carriers in the OLEDs. In addition, the impedance changes due to OLEDs degradation are analyzed. Using the proposed Impedance Spectroscopy Analysis method in this paper, the origin of degradation can be accurately and effectively separated from the state change of the interface and the buck. The results strengthen the existing interpretation of the interface trap effect of HTL/EML and showed that it can be traced with the rate of change of the extracted impedance value. Chapter 4 briefly introduces the program tool for analyzing the OLEDs used in this paper, and attached an appendix for derived the formula. And I will discuss the possibility of applying this Impedance Spectroscopy Analysis to mass products industry in the future.본 논문은 임피던스 분광법을 이용한 유기 발광 다이오드의 특성 분석 방법에 대한 연구이다. 일반적으로 유기 발광 소자는 TCO (Transparent Conductive Oxide)와 금속 전극 사이에 발광에 필요한 유기 물질이 얇게 적층 된 구조를 갖는다. 유기 물질의 화학적 취약성과 헤테로 접합의 복잡성으로 인해 파괴적인 방식 보다는 비파괴 방식으로 제조된 유기 발광 다이오드의 특성을 조사해야 한다. 고전적으로, 전류-전압계를 사용하여 전류-전압 곡선을 측정하고 휘도 계를 사용하여 발광을 측정하는 방법이 OLEDs의 특성을 평가하는데 사용된다. 그러나 OLEDs의 인터페이스 상태 또는 캐리어 동역학에 대한 세부 사항을 조사하기 위해서는 작동 조건 하에서의 임피던스 응답을 측정해야 한다 일반적인 고체 물리에서의 임피던스 분석 방법은 커패시턴스에 주로 초점을 맞추고 있는 반면에, 임피던스 분광법 (IS)은 miliherz 에서 megaherz의 주파수 범위에서 모든 임피던스 응답을 다루는 것이 특징이다. 이를 통해 분해능이 높은 등가 회로를 구성하고 각각 측정 된 임피던스를 면밀히 분석 할 수 있다. 각 임피던스는 작동 직류 전압을 결정한 후 교류 소신호를 인가하여 측정되는데, 이 작동 직류 전압과 교류 소신호는 소자의 동작을 적절히 설명하기 위해 전략적으로 선택되어야 한다. 제 1 장에서는 임피던스 분광 분석의 개요를 소개하고 임피던스 측정 방법의 배경을 설명한다. 그리고 임피던스 분석 방법을 OLEDs에 적용하려는 동기에 대해서 설명하고 임피던스 분광학을 통해 OLEDs의 특성을 분석하는 다양한 방법들이 논의된다. 제 2 장은 OLEDs의 임피던스 분석 방법에 대해 이전에 보고된 논문을 검토하고 이들 논문의 한계를 설명한다. 특히, 이전에 과소평가된 확산 캐패시턴스의 기여는 OLEDs의 특성을 결정할 때 오류를 방지하는 데 매우 중요하다는 것을 보여줄 것이다. 이러한 확산 용량을 설명하기 위해 Laux & Hess 모델이 적용되었다. 이 모델은 잔류 전류에 대한 임피던스 응답을 매우 잘 설명 할 수 있고 심지어 음의 커패시턴스 현상도 잘 설명해 준다. Laux & Hess 모델을 사용한 분석 결과는 작동 중의 OLEDs의 특성을 잘 묘사 하고 있음을 보였고 이 모델의 분석 방법을 위한 근사 프로세스를 제안하였다. 제 3 장에서는 ITO/a-NPD[N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-2,2′-dimethylbenzidine]/Alq3[Tris-(8-hydroxyquinolinato)aluminum]/LiF/Al 형 OLED를 제작하여 제 2 장에서 제안된 개선된 임피던스 분석법을 사용하여 조사하였다. 먼저, 구조적(두께) 변화에 따른 임피던스 응답의 변화를 측정하여 물리적, 정량적 해석이 수행되었다. 높은 주파수에서 측정된 임피던스는 OLEDs의 인터페이스 및 버크 특성을 나타내며 저주파수에서의 임피던스는 OLEDs의 캐리어의 동적 이동을 설명한다. 또한 OLEDs의 열화로 인한 임피던스 변화를 분석하였다. 본 논문에서 제안 된 Impedance Spectroscopy Analysis 방법을 사용하면, 열화의 원인으로서 계면과 버크의 상태 변화가 정확하고 효과적으로 분리 될 수 있다. 결과는 HTL/EML의 인터페이스 트랩 효과에 대한 기존 해석을 강화하는 것으로 나왔고 추출된 임피던스 값의 변화율을 추적 할 수 있음을 보여 주었다. 4 장 에서는 이 논문에서 사용된 OLEDs를 분석하기 위한 프로그램 도구를 간략하게 소개하고 수식에 대한 부록을 첨부 했다. 그리고 향후 이 임피던스 분광학 분석을 산업에 적용 시킬 가능성에 대해 논의하고 요약하도록 하겠다.Abstract i Contents v List of Figures viii List of Tables xiii Chapter 1 Introduction 1 1.1 Motivation 1 1.1.1 History of Organic Light Emitting Diodes 6 1.1.2 OLEDs Hetero Structures 8 1.1.3 OLEDs life time 11 1.2 Materials 15 1.2.1 Alq3 16 1.2.2 HAT-CN 17 1.2.3 α-NPB 18 1.2.4 DCM 19 1.3 Equipment & Instrument 20 1.3.1 Thermal Evaporator 20 1.3.2 Impedance Measurement Equipment for OLEDs 23 Chapter 2 Analytic Theory of OLED Impedance Spectroscopy 26 2.1 Problems of Previous Reported Impedance Spectroscopy to extract parameter on OLEDs 28 2.2 Complex Capacitance Concepts for IS 31 2.2.1 ARC 31 2.2.2 ZARC 34 2.2.3 Negative Capacitance 38 2.2.4 Equivalent circuit strategy for OLEDs 43 2.3 Theory 45 2.3.1 Impedance Spectroscopy 45 2.3.2 Small-Signal Model 49 2.3.3 Complex Plane Diagram 51 2.3.4 Equivalent Circuit Modeling 54 2.3.5 Superposition of various Impedance Component 58 2.3.6 Debye relaxation plot( -plot) 60 2.4 How to extract reasonable parameter from impedance spectroscopy 64 Chapter 3 Experiments 71 3.1 Thickness modification OLEDs 72 3.1.1 Analysis of the Interface of the OLEDs 76 3.1.2 Analysis of the Carrier Distribution of OLEDs 78 3.2 Thickness ratio modification 80 3.2.1 Relation between efficiency and M-plot 82 3.3 DCM doping ration Modification 84 3.3.1 Correlation between Current-Voltage-Efficiency and Impedance Response 84 Chapter 4 Discussion 90 4.1 Consideration of Effects of Interface Properties 90 4.2 Consideration of Effects of Bulk properties 92 4.3 Negative Capacitance relation with efficiency analysis 93 4.4 Mobility Measurement Using Impedance analysis 96 Chapter 5 Conclusion 101 Appendix 109 Bibliography 116 Publications 122 초 록 127Docto