Influence of bending radius on the properties of flexible AMOLED displays

Choosing a suitable bending structure is an important way to optimize flexible AMOLED. In this article, we proposed and established a drop-shape model through nonlinear finite element analysis software, comparing it with the “U”-shaped bending model. The mechanical stress conditions under different bending radius are analyzed and compared. Aiming to find a better module folding track, we output the influence of the bending radius on the stress and strain of the device layer, so that these data and research can provide reliable support for future material selection and structural optimization. The super-elastic and viscoelastic behaviors of optically clear adhesive are described by polynomial reduced integral and Prony series model, respectively. Both U-shaped various layers of film and overall flexible screen module strains increase fast with the decreasing of bending radius and smaller radius will increase the fatigue damage risk. The stress and strain of the drop shape did not change significantly with the decrease of the radius. During the bending process, the most stressed part appears in the outermost TP layer. In a small radius, it can be optimized from a curved structure, and water drop and wedge shapes can be prioritized.     

Highly reliable a‐IGZO TFTs on a plastic substrate for flexible AMOLED displays

We have successfully reduced threshold voltage shifts of amorphous In–Ga–Zn–O thin‐film transistors (a‐IGZO TFTs) on transparent polyimide films against bias‐temperature stress below 100 mV, which is equivalent to those on glass substrates. This high reliability was achieved by dense IGZO thin films and annealing temperature below 300 °C. We have reduced bulk defects of IGZO thin films and interface defects between gate insulator and IGZO thin film by optimizing deposition conditions of IGZO thin films and annealing conditions. Furthermore, a 3.0‐in. flexible active‐matrix organic light‐emitting diode was demonstrated with the highly reliable a‐IGZO TFT backplane on polyimide film. The polyimide film coating process is compatible with mass‐production lines. We believe that flexible organic light‐emitting diode displays can be mass produced using a‐IGZO TFT backplane on polyimide films.     

Alleviation of abnormal NBTI phenomenon in LTPS TFTs on polyimide substrate for flexible AMOLED

This letter investigates the negative‐bias temperature instability (NBTI) behavior of p‐channel low‐temperature polycrystalline silicon thin‐film transistors (LTPS TFTs) on plastic substrate. The measurements reveal that the threshold‐voltage positive shift is highly correlated to the passivation of grain boundary trap states. By applying the established phenomenon such as NBTI recovery and H diffusion from PI substrate, a new model is introduced to explain the mechanism and verified by the experiment. With the thick buffer and bottom metal layer or newly processed PI substrate, we succeeded in adjusting the NBTI behavior of LTPS TFTs on plastic substrate.     

5.8‐inch QHD flexible AMOLED display with enhanced bendability of LTPS TFTs

By applying the curve‐type thin film transistor (TFT) with longitudinal strain, TFT parameters do change little down to the 2R bending. The mobility variation range reduces down to 4% compared with 28% of the line‐type channel with transverse strain. The smaller variation is preferred for a high quality display. We clarified that majority carrier's effective mass and scattering rate are dominant factors influencing the bended TFT's performance, which can be controlled by the strain orientation and channel shape. This understanding and improvement was embedded in the 5.8″ flexible QHD active matrix organic light emitting diode panel with multi edge curvature of Galaxy S8. Through this achievement, we made our flexible premium active matrix organic light emitting diode panels more performable, reliable, and highly productive in small R bending circumstance.     

Vacuum chucking assist sheet for fixing flexible sheets during the printing process

A vacuum chuck is often used to fix substrates in the field of electronic device fabrication including printing of the device electrodes. A conventional vacuum chuck plate locally sucks only where suction holes exist. However, when we employ a film as the substrate to be printed, suction from the holes causes the film distortion, which results in misprinting. Thus, we have newly developed a chucking assist sheet to fix a film substrate on a vacuum chuck stage for high-quality electrode printing. When printing is performed, the sheet is located between the film substrate and the vacuum chuck stage. The developed sheet is composed of lower and upper layers of woven stainless steel mesh and non-woven fabric, respectively, and such a structure can significantly decrease misprinting resulting from the film distortion caused by suction. In the present paper, we present the design concept of this chucking assist sheet and details of its features.     

Correlation analysis of a discrete-time flexible arrival process

In this paper, a flexible discrete-time arrival process is introduced and its correlation properties are analyzed. The arrival process is the so-called batch-on/off model, an extension of the original on/off source used in the context of ATM networks. In the batch-on/off model, a group of arrivals may be generated at any given active slot. General distributions are assumed for the three input random variables characterizing the process: busy and idle periods, and batch size. The analysis focuses on two related processes: the process of counts and the sequence of interarrival times. For each process, an exact closed-form expression of its complete autocorrelation function is obtained. Explicit algorithms are provided to compute both autocorrelation functions, which are numerically evaluated for different distributions of the busy and idle periods and the batch size. The results provided in this paper reveal the analytical tractability of these models which, in addition to their flexibility, makes them very suitable for the performance evaluation of discrete-time communication systems and for general research in the area of queuing theory.     

Improvement in image quality of a 5.8‐in. OTFT‐driven flexible AMOLED display

Abstract— The image quality of an OTFT‐driven flexible AMOLED display has been improved by enhancing the performance of OTFTs and OLEDs. To reduce the operating voltage of OTFTs on a plastic film, Ta²O⁵ with a high dielectric constant was used as a gate insulator. The organic semiconductor layer of the OTFT was successfully patterned by a polymer separator, which is an isolating wall structure using an organic material. The OTFT performance, such as its current on/off ratio, carrier mobility, and spatial uniformity on the backplane, was enhanced. A highly efficient phosphorescent OLED was used as a light‐emission device. A very thin molybdenum oxide film was introduced as a carrier‐injection layer on a pixel electrode to reduce the operating voltage of the OLED. After an OTFT‐driven flexible AMOLED display was fabricated, the luminance and uniformity on the display was improved. The fabricated display also showed clear moving images, even when it was bent at a low operating voltage.     

Advances in backcalculating the mechanical properties of flexible pavements

In current practice, the evaluation of the performance of existing road pavements has become a priority issue for many highway engineers. To make appropriate rehabilitation and management decisions the engineer must rely on an efficient method for determining the structural conditions of pavements. Nondestructive testing (NDT) reveals the stress–strain properties of pavement layers at relatively low strain levels. Since the theoretical approaches used to determine the stress–strain relationships in pavement layers calculate the deflections for given mechanical properties, it is necessary to make an inversion using a backcalculation tool. Several methods have been developed to backcalculate the mechanical properties of flexible pavement; these methods vary in analysis type, material model, and optimization algorithm. This study is designed to explain these methods and to compare and contrast them in terms of modeling precision, computational expense, and calculation details. Consequently, innovations and advances in backcalculating flexible pavements are considered in this paper.     

Characterizing the impact of process variation on 45 nm NoC-based CMPs

Current integration scales make possible to design chip multiprocessors with a large amount of cores interconnected by a NoC. Unfortunately, they also bring process variation, posing a new burden to processor manufacturers.Regarding the NoC, variability causes that the delays of links and routers do not match those initially established at design time. In this paper we analyze how variability affects the NoC by applying a new variability model to 100 instances of an 8 × 8 mesh NoC synthesized using 45 nm technology. We also show that GALS-based NoCs present communication bottlenecks due to the slower components of the network, which cause congestion, thus reducing performance. This performance reduction finally affects the applications being executed in the CMP because they may be mapped to slower areas of the chip. In this paper we show that using a mapping algorithm that considers variability data may improve application execution time up to 50%.     

Random behaviors in the process of immunological memory

We have used a system of coupled maps to study random variations in the immune memory process and the possible network immune memory that can remain for long time in the absence of antigenic stimulation through the idiotypic–anti-idiotypic interactions. Our approach describes the behavior of the immune network proposed by Jerne and considers that the cell–cell interactions routine results in maintenance of memory in a dynamic equilibrium. The critical values of the concentrations of antigens for the validity of the model and a phases diagram with three different phases are also obtained.     

Distributed control of a class of flexible mechanical systems with global constraint

In this paper, the constrained problem is investigated for both flexible string model and Euler–Bernoulli beam model with the tip payload, based on an infinite dimensional generalisation of a distributed control method. The control objectives are to develop the control law so that the motion of flexible mechanical systems can track a desired reference signal, and ensure that the string or beam remain in a constrained space. We prove that, with the proposed control, the tracking error is exponentially stable without violation of the constraint. The proof of convergence is based on an Integral-Barrier Lyapunov Function (IBLF), and extensive simulations are provided to illustrate the performance of the control system.     

Modeling and analysis of touch on flexible ultra-thin touch sensor panels for AMOLED displays employing finite element methods

The work employs the finite element method (FEM) to model the touch on the flexible ultra-thin touch sensor panel for analyzing touch characteristics and signals. Touch sensor panel readout circuits typically depend on touch signals to determine whether the touch sensor panel is touched or not. However, the ultra-thin touch sensor panel encountered a problem which cannot correctly recognize touch points on this type of touch sensor panel (TSP) on active-matrix organic light emitting diodes (AMOLED) displays since its electrical characteristics are different from the one of the conventional TSP. The modeling techniques for the flexible ultra-thin touch sensor panel on an AMOLED display is used to analyze touch signals from the influence of the thickness of top over layer of the flexible ultra-thin TSP and to observe the variations of mutual capacitance from touch on the flexible ultra-thin TSP. When the flexible ultra-thin touch sensor panel with the thickness of the top over layer less than the threshold thickness of the top over layer is on multi-touch, the phenomenon of the ghost points are generated. The simulation to find the threshold thickness of the top over layer based on the FEM model is conducted, and the simulation results show the top layer thickness should be larger than 107 µm to eliminate the ghost points. Furthermore, a new solution that is an optimization of the electrode pattern of transmitters and receivers in the ultra-thin touch sensor panel to further minimize the threshold thickness of the top over layer of TSP without changing the physical structure of TSP is proposed. The results conducted by using this proposed solution show that TSP top over layer threshold thickness can be reduced to 65 µm without appearance of the ghost points.

     

剪刀式折叠桥梁展桥机构架桥过程力学状态分析

为了获得剪刀式折叠桥关键铰点在架桥过程中受力情况,利用Denavit-Hatenberg齐次变换矩阵建立了展桥机构的运动学模型,然后通过立学平衡方程建立展桥机构的力学模型,得到典型姿态下关键铰点的受力情况。利用虚拟样机技术对剪刀式折叠桥梁展桥机构展开过程进行了仿真分析,验证了模型的正确性。结果表明,展桥机构的关键铰点在架桥过程中将受到交变载荷的作用(对液压系统产生较大冲击)。其中,中桥节翻转油缸所连接铰点受力最大,对液压系统造成影响最大,与样机展桥油缸在实验时发生间歇性溢油现象相吻合。研究结果为展桥机构优化设计打下基础。     

Optimization process for configuration of flexible joined-wing

An optimized configuration design utilizing both structural and aerodynamic analyses of a flexible joined-wing configuration is presented in this paper. The joined-wing aircraft concept fulfills a proposed long-endurance surveillance mission and incorporates a load-bearing antenna structure embedded in the wing skin. Aerodynamic, structural, and optimization analyses are completed a number of times. A range of joined-wing configurations were trimmed for critical flight conditions and then structurally optimized for trimmed flight and gust loads to achieve a minimum weight for each configuration. A response surface statistical analysis was then applied to determine optimal joined-wing aircraft configurations. The response surface showed trends in the design of lightweight joined-wing aircraft. The revised version of this paper was presented at the 10th MAO Multidisciplinary Analysis and Optimization Conference, August 30–September 1, 2004.     

Interdiffusion behaviors and mechanical properties of Cu-Zr system

In this work, solid-to-solid diffusion couples were assembled and annealed to investigate diffusion behavior and mechanical properties of the Cu-Zr system in temperatures range from 1043 K to 1113 K. Six intermetallic compounds (IMCs) Cu₉Zr₂, Cu₅₁Zr₁₄, Cu₈Zr₃, Cu₁₀Zr₇, CuZr, and CuZr₂ were observed in the diffusion zone. Composition-dependent interdiffusion coefficients of IMCs have been calculated based on the measured composition Cu profiles of the diffusion zones by using Sauer–Freise method. And the average effective interdiffusion coefficients for each phase were also calculated by using Wagner method. The activation energies of diffusion are evaluated according to the average effective interdiffusion coefficient. Finally, the load-displacement curves measured by nano-indentation are obtained to characterize mechanical properties of Cu₉Zr₂ and Cu₅₁Zr₁₄, which have similar hardness and elastic moduli.     

Evolving neural controllers that elicit nontrivial behaviors using a developmental process

Recently, evolutionary robotics (ER) has been attracting a lot of attention in the field of robotics artificial life and so on. ER approaches are expected to provide feasible methods to design controllers for autonomous mobile robots with less human intervention. However, most of the conventional studies in ER have been aiming at obtaining very simple (trivial) behaviors such as obstacle avoiding, wall following, and target approaching. To make the ER approach more fruitful, we should pay close attention to obtaining nontrivial behaviors. Based on these considerations, in this paper we propose a method for obtaining nontrivial behaviors using a developmental process with a carefully arranged grafting method. To verify the validity, we apply our idea to the construction of neural controllers that can cope with rough terrain. This work was presented, in part, at the Third International Symptosium on Artificial Life and Robotics, Oita, Japan, January 19–21, 1998     

Evaluating the learning process of mechanical CAD students

There is little theoretical or experimental research on how beginner-level trainees learn CAD skills in formal training sessions. This work presents findings on how trainees develop their skills in utilizing a solid mechanical CAD tool (Pro/Engineer version 2000i² and later version Wildfire). Exercises at the beginner and intermediate levels were designed so that several variations of a solid object are built by non-experienced trainees as they accumulate training time. In this case, trainees are fourth year mechanical engineering seniors and as such, they were of a similar technical and gender make-up. This assessment was conducted over the duration of training (16-week long semester). The test exercises were used to assess the trainees’ speed and proficiency in the use of CAD by (1) measuring their performance time and (2) feature count (number of features-of-size used to build the test parts). Using performance time data, empirical learning curves are generated. Breaking these curves into declarative and procedural components provides insight into how fast the trainees develop cognitive and motor CAD skills. In order to confirm that this methodology can be extended to other CAD platforms, a follow-up study was performed on a different set of beginner-level trainees with similar make-up while using the same beginner-level parts but with a more recent version of Pro/Engineer: Wildfire. One significant result of this study is that the procedural and declarative components of CAD learning are largely cognitive.     

Characterization and compensation of OLED aging in a digital AMOLED system

Organic light‐emitting diode (OLED) aging is the root cause for image sticking artifact and considered as the toughest problem besides the low yield problem of active‐matrix organic light‐emitting diode (AMOLED) displays. Digital driving can eliminate Mura artifact and allow a similar yield like LCD. However, it is more prone to OLED aging than analog driving, so that the lifetime will become shorter. In this paper, we pursue the approach to measure the pixel current and compensate OLED I–V drift. Information gained from electrical measurements during the lifetime of the display may be correlated to electro‐optical drift, particularly the current efficiency. The aging model has to consider the dependence of I–V drift and efficiency loss on the operation point/voltage for each subframe. Specific compensation algorithms have been developed. Two AMOLED prototypes (1.5 and 2.8 in.) were validated. Burned‐in pattern can be compensated, so the concept has been proven as effective. With the method described in this paper, digital AMOLED may reach a similar and even significantly higher lifetime than an analog AMOLED.