AMOLED Research Articles

Simulated and experimental demonstrations of interfacial adhesive strength for released layer utilized in flexible electronics

Interfacial adhesive strength is an important characteristic considered in multilayered active-matrix organic light-emitting diode (AMOLED) architecture as it has an impact on the mechanical reliability issue generated from complicated organic/inorganic hybrid lamination and final debonding procedure. Thus, an appropriate released layer design is needed to manage the capability and reliability of the encapsulated AMOLED structure de-bonded from the temporary carrier. Accordingly, this research utilizes the plasma-assisted surface modification to improve the interfacial adhesive strength of the polyimide (PI)/debonding layer (DBL) during mechanical debonding. In addition, a fracture-based finite element model of peeling testing architecture is constructed to analyze the adhesive behavior of the PI/DBL interface via the utilization of the modified virtual crack closure technique. The analytic results indicate that the suitable plasma-assisted surface modification significantly increased the nitrogen concentration and generated the high dissociation energy N–O bonds among the bonded interface between the PI/DBL thin films. The opening mode-fractured energy also takes the dominance proportion in the entire peeling load-induced interfacial energy release rate. The application of plasma-assisted surface modification enhanced the delamination resistance of the concerned interface and maintained the structural stability during the lamination and related release of a whole flexible AMOLED architecture.

An AMOLED Pixel Circuit Based on LTPS Thin-film Transistors with Mono-Type Scanning Driving

Using low-temperature poly-silicon thin-film transistors (LTPS TFTs) as a basis, a pixel circuit for an active matrix organic light-emitting diode (AMOLED) with narrow bezel displays was developed. The pixel circuit features mono-type scanning signals, elimination of static power lines, and pixel-integrated emitting control functions. Therefore, gate driver circuits of the display bezel can be simplified efficiently. In addition, the pixel circuit has a high-resolution design due to an increase of the pulse width of the scan signal to extend the threshold voltage and internal–resistance drop (IR drop) detection period. Further, regarding the influences of process–voltage–temperature (PVT) variation in the pixel circuit, comparison investigations were carried out with the proposed circuit and other pixel circuits with mono-type scanning signals using Monte Carlo analysis. The feasibility of the proposed pixel circuit is well demonstrated, as the current variations can be reduced to 2.1% for the supplied power reduced from 5 V to 3 V due to IR drop, and the current variation is as low as 10.6% with operating temperatures from –40 degrees to 85 degrees.

Micropropagation of Turkestan Soap Root Allochrusa gypsophiloides – Natural Source of Saponins

Allochrusa gypsophiloides or Turkestan soap root (TSR), which is endemic to Central Asia, is a valuable saponin-bearing technical and medicinal plant. The purpose of this study was to develop in vitro mass propagation for the conservation of endangered species. Node explants were induced to regenerate adventitious shoot buds on Murashige and Skoog medium (MS) supplemented with different concentrations of 6-benzylaminopurine (BAP) and/or kinetin in combination with naphtylacetic acid (NAA). The maximum number of shorter shoots per explant (16.8 ± 3.1) was recorded on MS contained 0.5 mg/L BAP and 0.5 mg/L NAA after one month cultivation. For elongation, obtained shoot conglomerates were transfered for hormone-free MS. The cultivation of initial explants on MS with kinetin led to a three-fold reduction in the number of shoots characterized by a maximum length and clearly defined internodes (without the stage of elongation). Micropropagation was achieved by cutting obtained shoots and adventitious shoot induction. The maximal shoot proliferation (62 ± 6.9) on MS 0.5 mg/L BAP + 1.0 mg/L kinetin + 0.5 mg/L NAA was obtained. Shoots of about 0.5 cm required to elongation before rooting on the liquid ½ MS medium contained NAA or IBA. In both cases, auxin concentration 2.0 mg/L induced maximal rooting (58 % and 60 %, respectively) at 20-day’s incubation. Type of auxin was influenced most on root quality (thickness, color, branching) than on their frequency and number.

An Area-Efficient 10-Bit Buffer-Reused DAC for AMOLED Column Driver ICs

In this paper, we proposed an area-efficient 10-bit digital-to-analog converter (DAC) with buffer-reusing method to dramatically relief the severe area exploding issue in high-definition active-matrix organic light-emitting diode (AMOLED) driver integrated circuits (ICs). In our design, we implement the functionalities of a large number of switches and capacitors in conventional DAC by a compact internal buffer. Furthermore, we minimize the buffer capacity requirement by elaborately reusing the indispensable output buffer in the typical column driver. In this way, we can cut down nearly a half of the decoder-switches and simultaneously reduce the capacitor size from 8 C to 3 C without designing an intricate and power-consuming amplifier separately. A prototype 6-channel column driver employing the proposed buffer-reused DAC was fabricated by 0.35 μm 2P3M BCD (Bipolar, CMOS, DMOS) process and its effective layout area per channel is 0.0429 mm2, which is 42.8% smaller than that of the conventional 10-bit R-C DAC. Besides, the measured differential nonlinearity (DNL) and integral nonlinearity (INL) are 0.514 LSB/0.631 LSB, respectively and the maximum value of inter-channel deviation voltage output (DVO) is 3.25 mV. The settling time within 5.6 μs is readily achieved under 1.5 kΩ-resistance and 100 pF-capacitance load. Measurement results indicate that the proposed buffer-reused DAC can successfully minimize the die area while maintaining other required performances.

Interfacial fracture investigation of patterned active matrix OLED driven by amorphous-Si TFTs under film-type packaging technology

Considering the structural stability for active-matrix organic light-emitting diode (AMOLED) application, the reliability of lamination interfaces has become a major concern. The comprehensive influence of structural design integrated with material selections should be carefully examined and estimated. The layout effect of embedded pattern defined layer (PDL) plays an important role in the actual AMOLED architecture. To address the issue of stress-induced failure mechanism of PDL under external loads due to external bending, fracture mechanics-based finite element analysis integrated with Tsai–Hill criterion is utilized in this research. Simulated results indicate that the declined thickness and 45° oblique angle design for PDL prevents the failure occurrence of concerned interfaces. Notably, multiple neutral axis (NA) occurs when an extra-low Young’s modulus of pressure-sensitive adhesive (PSA) is considered. Multiple NA design prevents brittle fracture failure occurrence in gas barrier architecture, while these multiple NAs shift to adjust to the foregoing location. Accordingly, a proper arrangement of these multiple NAs in AMOLED packaging encapsulation through the selection of material characteristics and stacked thickness of PSA thin film has the advantage to enhance structural reliability.

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene Doped Lithium Carbonate as an Effective Electron Injecting Layer for Both Inverted and Conventional Organic Light-Emitting Diode Structures

High driving voltage, low power efficiency, and insufficient device stability are the most critical complications for organic light-emitting diodes (OLEDs) on their way to practical applications. Particularly in the case of active-matrix organic light emitting device (AMOLED) displays, inferior electron injection from commonly-used ITO electrodes is a critical issue. In this work, 2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Li2CO3) is used as an effective electron injecting layer for both inverted and normal bottom-emission organic light-emitting diodes. When the concentration of Li2CO3-doped MADN is optimized, the device exhibits improved characteristics, including improvements in turn-on voltage, luminance, and efficiency. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses reveal an energy level shift in MADN:Li2CO3, which indicates the Fermi level of MADN is moving close to its lowest unoccupied molecular orbital (LUMO) and therefore facilitating electron injection from ITO. In addition, the AFM measurement showed the morphology of the Li2CO3-doped MADN films, revealing good thermal stability in the material related to enhanced lifetime. The results unveiled in this work indicate that Li2CO3:MADN is a promising electron injecting layer for OLEDs with different device structures and provide a vision of the mechanisms behind this phenomenon.

Flexible and Transparent Thin-Film Transistors Based on Two-Dimensional Materials for Active-Matrix Display.

Two-dimensional (2D) materials have attracted significant attention because of their outstanding electrical, mechanical, and optical characteristics. Because all of the conducting (graphene), semiconducting (molybdenum disulfide, MoS2), and insulating (hexagonal boron nitride, h-BN) components can be constructed from 2D materials, thin-film transistors based on 2D materials (2D TFTs) have been developed. However, scaling-up is necessary for these technologies to go beyond their initial implementation using the mechanical exfoliation method. Furthermore, it would be beneficial to find a method to realize high flexibility and/or transparency to their full potential. In this study, large-scale, flexible, and transparent 2D TFTs are developed and demonstrated as a backplane in active-matrix organic light-emitting diodes (AMOLEDs). With the optical chemical vapor deposition of the 2D materials, flexible (bending radius < 1 mm) and transparent (transmittance > 70%) TFTs with high electrical performances (mobility ≈ 10 cm2 V-1 s-1, on/off current ratio > 106) can be achieved. Furthermore, 2D TFTs are integrated into OLEDs by connecting the source electrode of the TFT to the anode of the OLED via a single graphene film, thus demonstrating pixel-by-pixel driving through a 2D TFT array in an active-matrix configuration.

A Temperature Compensation Method by Adjusting Gamma Voltages for High Luminance Uniformity of Active Matrix Organic Light-Emitting Diode Displays

In this paper, a temperature compensation method is proposed for active-matrix organic light-emitting diode (AMOLED) displays to achieve high luminance uniformity over a wide operating temperature range. The proposed temperature compensation method compensates for variation in OLED luminance according to temperature by adjusting the gamma voltages. To verify the proposed method, a built-in test circuit, which includes temperature sensors, current calculation block, current adjustment block, and gamma voltage generator, was fabricated using 90 nm complementary metal-oxide semiconductor process technology with 6 V high-voltage devices. The measurement results show that the proposed method achieves a high luminance uniformity with an OLED luminance variation of less than 1.54 cd/m 2 over the temperature range of -45°C to 60°C. Therefore, the proposed temperature compensation method is suitable for AMOLED displays requiring high luminance uniformity.

Real RGB printing AMOLED with high pixel per inch value

AbstractA 403‐ppi (pixel per inch) real RGB active‐matrix organic light‐emitting diode (AMOLED) was fabricated without using fine metal mask (FMM). Organic light‐emitting materials were printed on array panel, with a novel process that has the advantages of low cost and high pixel density. The uniformity of the organic light‐emitting diodes (OLEDs) was improved with carefully tuning printing parameters, and good panel performance was achieved. The key to such a process was the design of the hexagonal patterning of the pixels. The image quality of the panel with this hexagonal pixel arrangement was evaluated with a bmp format Pixel Layout Simulation picture.

Low Energy-Consumption Inverted Orange Organic Light-Emitting Diodes with Reduced Efficiency Roll-Off

Inverted organic light-emitting diodes (IOLEDs) have a bottom cathode, making them convenient to integrate with the preferred n-type active matrix OLED driving technologies. Furthermore, inverted OLEDs show much better air-stability compared with conventional OLEDs, due to the very reactive and sensitive of alkali doped electron injection layer (EIL) towards ambient oxygen and moisture. For inverted OLEDs, the bottleneck to limit their efficiency and stability is the interface at cathode/EIL and light emitting layer (EML)/charge transporting layer. In this paper, we have investigated the effect of different electron/hole transporting layers on the turn-on voltage, efficiency roll-off and power consumption of inverted orange OLEDs. We found that the device exhibits extremely-low efficiency roll-off and a significant lifetime improvement.

Self assembled cathode patterning for AMOLED

Self assembled cathode patterning for AMOLED

Self assembled cathode patterning for AMOLED

Self assembled cathode patterning for AMOLED

Transparent AMOLED Display Derived by Metal Oxide Thin Film Transistor with Praseodymium Doping

Transparent AMOLED Display Derived by Metal Oxide Thin Film Transistor with Praseodymium Doping

P-type LTPS Gate Driver to Generate Simultaneous and Overlapping Progressive Outputs for High-Resolution AMOLED Displays

P-type LTPS Gate Driver to Generate Simultaneous and Overlapping Progressive Outputs for High-Resolution AMOLED Displays

P-type LTPS Gate Driver to Generate Simultaneous and Overlapping Progressive Outputs for High-Resolution AMOLED Displays

P-type LTPS Gate Driver to Generate Simultaneous and Overlapping Progressive Outputs for High-Resolution AMOLED Displays

Transparent AMOLED Display Derived by Metal Oxide Thin Film Transistor with Praseodymium Doping

Transparent AMOLED Display Derived by Metal Oxide Thin Film Transistor with Praseodymium Doping

Novel Compensation Pixel Circuit with Simultaneous Emission Driving Scheme for High-Resolution AMOLED Displays

Novel Compensation Pixel Circuit with Simultaneous Emission Driving Scheme for High-Resolution AMOLED Displays

New External Compensated Circuit with Buffer IC for High-Resolution AMOLED Displays

New External Compensated Circuit with Buffer IC for High-Resolution AMOLED Displays

New External Compensated Circuit with Buffer IC for High-Resolution AMOLED Displays

New External Compensated Circuit with Buffer IC for High-Resolution AMOLED Displays

Novel Compensation Pixel Circuit with Simultaneous Emission Driving Scheme for High-Resolution AMOLED Displays

Novel Compensation Pixel Circuit with Simultaneous Emission Driving Scheme for High-Resolution AMOLED Displays