AMOLED Research Articles

Low-voltage operatable top-gated organic transistors based on the solution-processed binary polymers dielectric for simplifying the manufacturing flow of arrayed AMOLED

The complex process flow is an important factor that hinders the development of active-matrix organic light-emitting diode (AMOLED) displays. Organic thin-film transistors (OTFTs) are one of the promising candidates as the pixel circuits for AMOLEDs. Both the architecture and the fabrication of OTFTs are crucial elements to determine the process flow and cost of the AMOLEDs. In this Letter, we develop a strategy to significantly simplify the process flow and reduce the cost of AMOLEDs by constructing top-gated OTFTs with a solution-processed vertically phase separated binary polymer dielectric as the pixel circuits. The design on the OTFTs considers both the process flow and the device performance in terms of mobility and operating voltages. The mechanism to improve device performances is discussed. Finally, a 3 × 4 arrayed AMOLED is demonstrated, in which a high mobility over 0.3 cm2/Vs is obtained on the switching and driving OTFTs, and luminance over 300 cd/m2 is achieved on the OLEDs at the supplied low operating voltages of 10 V. This strategy provides a competitive technological route for the manufacturing of AMOLEDs.

Vertically stacked skin-like active-matrix display with ultrahigh aperture ratio

Vertically stacked all-organic active-matrix organic light-emitting diodes are promising candidates for high-quality skin-like displays due to their high aperture ratio, extreme mechanical flexibility, and low-temperature processing ability. However, these displays suffer from process interferences when interconnecting functional layers made of all-organic materials. To overcome this challenge, we present an innovative integration strategy called “discrete preparation-multilayer lamination” based on microelectronic processes. In this strategy, each functional layer was prepared separately on different substrates to avoid chemical and physical damage caused by process interferences. A single interconnect layer was introduced between each vertically stacked functional layer to ensure mechanical compatibility and interconnection. Compared to the previously reported layer-by-layer preparation method, the proposed method eliminates the need for tedious protection via barrier and pixel-defining layer processing steps. Additionally, based on active-matrix display, this strategy allows multiple pixels to collectively display a pattern of “1” with an aperture ratio of 83%. Moreover, the average mobility of full-photolithographic organic thin-film transistors was 1.04 cm2 V−1 s−1, ensuring stable and uniform displays. This strategy forms the basis for the construction of vertically stacked active-matrix displays, which should facilitate the commercial development of skin-like displays in wearable electronics.

Driving scheme for residual image reduction in active-matrix organic light-emitting diodes display

Residual image is a frequent issue in active-matrix organic light-emitting diode (AMOLED) display, due to hysteresis effects of the internal devices. Up to now, some optimized methods have been researched mainly from process perspective. However, the approaches from driving scheme perspective and their electrical mechanism have rarely been demonstrated systematically. In this work, a technical proposal has been proposed to separate the influences of different devices including both thin film transistors (TFTs) and OLEDs furtherly. It was found that the current curve gap was nearly equal to the luminance curve gap and the main factor of residual image was shown to be the hysteresis of TFTs. An equivalent circuit of two thin film transistors and one capacitor (2T1C) was also adopted to substantiate the influences of threshold voltage (Vth) compensation for reducing residual image, and a series of experiments of tuning capacitance were carried out for corresponding compensation improvements. Moreover, other driving scheme optimizations were also studied to reduce residual image furtherly, including increasing the data input time and resetting the driving TFTs. The research opens the possibility of considering reduction of residual image from driving scheme perspective and more systemic analysis from the internal electrical mechanism in AMOLED display.

64‐2: The Effect of Poly Silicon Grain Boundary Reduction on LTPS Devices and Display Effects Applied to Flexible AMOLED

Low‐temperature polycrystalline silicon (LTPS) thin‐film transistor devices can be used as core components of pixel driving circuits for active matrix organic light‐emitting displays （AMOLED）. Poly silicon (P‐Si) film and device performance directly affects the display effect. This paper investigates polysilicon grain boundary reduction for LTPS devices on PI substrates, exploring the effects of grain boundary reduction on LTPS devices and image sticking. Reduction of polysilicon grain boundaries through optimization of a‐Si deposition process, a‐Si two‐step deposition and excimer laser annealing (ELA) doublescan process, ELA double‐scan process reduces grain boundaries by 67 %. We prepared LTPS devices with thinner gate interlayers (GI) based on P‐Si grain boundary reduction, LTPS devices with positive threshold voltage bias and increased mobility, AMOLED displays with thinner GI can have 23% better image sticking.

77‐3: Power‐Efficient and High‐Color‐Gamut RGBY AMOLED Displays

We present a novel four color sub‐pixel active matrix organic light emitting Device (AMOLED) display that uses only three OLED depositions while enabling very high color gamut with greatly reduced power consumption. Achieving 90% of Rec. 2020 color standard, power consumption is reduced by 39% compared to that of a conventional RGB side‐by‐side top emission (TE) pixel architecture.

P‐72: A Bidirectional Gate Driver Circuit with Scan Signal for Low‐Frame‐Rate LTPO AMOLED Displays

This paper presents a bidirectional gate driver circuit based on low‐temperature polycrystalline oxide thin‐film transistors for a low‐frame‐rate AMOLED display. Simulation results indicate the falling and rising times of the output waveform are all below 3.48 μs and 0.56 μs with the threshold voltage variations of TFTs, ensuring the stability of the proposed circuit. The output waveforms are also generated successfully for a frame rate of 1 Hz display panel and have no fluctuation in consecutive frames. Therefore, the proposed circuit is suitable for a low‐frame‐rate AMOLED display.

P‐219: Research on the Direction of Luminance Modulation at Small Angles Based on Micro Lens

The study investigated the variations in luminance of active‐matrix organic light‐emitting diodes (AMOLED) when viewed at small angles, employing different micro lens arrangements. By examining the micro lens array (MLA) structure, we analyzed how luminance behaves at various angles. Concurrently, we explored the alignment of red, green, and blue (R/G/B) pixel apertures with the micro lens placement, aiming to achieve precise luminance modulation for acute viewing angles.Initially, micro lens arrays are crafted by utilizing materials with varying refractive indices above the pixel aperture, ensuring total internal reflection of light at thejunction between materials of high and low refractive indices. This arrangement also alters the emission angle of light. Within this architecture, the critical angle — determined by the disparity in refractive indices — and the variance in the angle at the reflective interface are crucial in influencing light emission reflection.Furthermore, we explored how the spacing of graphic openings with low refractive indices influences the angle of light emission. This spacing affects the reflection angle, as it is not produced by a singular interface but rather by a composite of multiple angles. The size of the pixel apertures and the spacing of these openings cause the point of total internal reflection to vary, altering the deflection angle of light. Thus, the design of pixel openings and the external expansion is crucial to controlling the light emission angle.Lastly, we examined the influence of the reflective interface and the external expansion design on the light output angle. This analysis highlighted the enhancement of light output at narrow angles and provided strategies to minimize luminance fluctuations at such angles, contributing to the development of high‐precision luminance control in AMOLED displays.

80‐4: Highly Reliable, As‐Grown Crystalline InGaZnO TFTs by Spray Pyrolysis for Low‐Cost Manufacturing of High‐Resolution AMOLED Display

We report a low‐cost method for growing highly‐oriented crystalline InGaZnO (C‐IGZO) for a high‐resolution, active‐matrix thin‐film transistor (TFT) backplane for organic light‐emitting diode displays using spray pyrolysis. The self‐aligned, coplanar oxide TFT with an as‐grown C‐IGZO channel layer demonstrates a threshold voltage of‐0.35 V, saturation mobility of 33.99 cm2 V‐1 s‐1 , and subthreshold swing of 0.15 Vdec‐1, with an on/off current ratio exceeding 108 . Moreover, the C‐IGZO TFT with a channel length of 1.16 μm exhibits excellent operational stability under bias temperature stress.

14‐2: Development of High Mobility and Reliability Metal Oxide TFT for 13.2 inch AMOLED Display

The 13.2 inch AMOLED panel with 262 ppi has been fabricated with the high mobility metal oxide TFTs (thin film transistors). The high mobility oxide TFTs have high mobility ~34cm2 /Vs. On Gen. 6 glass, a small Vth variation with channel length 3.5um has been obtained. Moreover, the high mobility oxide TFT shows small Vth shift under positive/negative bias temperature stress (PBTS/NBTS).

55‐1: A Novel Modeling & Compensation Algorithm for Medium‐Term Image Sticking on AMOLED Display

In this paper, we discuss the different type of image sticking(IS) and propose a novel algorithm for improving medium‐term IS on AMOLED display. This method could not only solve the IS effect on traditional display but also the multi‐areas frame rate (MAFR) display.For future OLED power‐saving applications, the application of MAFR becomes increasingly important. This involves categorizing the same display into high and low refresh rate zones based on display usage efficiency. When the display remains static for a period and then switches, the issue of display retention may arise. Our experimental results confirms that IS can be quantified into a model, and the algorithm is used for real‐time compensation to reduce the retention issues.

P‐34: The Effect Analysis of Display Quality According to the AMOLED Pixel Arrangement

In the AMOLED display, many factors affect the user's visual perception, such as color ratio, refresh rate and drive ability of array circuit, pixel density and so on. In the past, the primary idea to improve the precision and smoothness of the display quality is to increase the pixel per inch (PPI) and optimize the sub pixel rendering (SPR) algorithm between pixel units. At present, the PPI has gradually stabilized at 400+ grade for mobile phone display, and the IC driver algorithm corresponding to the pixel arrangement of each panel factory has also stabilized gradually, therefore, more efforts are needed to optimize the pixel arrangement itself to further improve the quality of display panel without taking into account the above two factors. Bear this in mind, we systematically summarized the common pixel patterns to extract the key characteristics of pixel arrangement benefited to the display quality by simulating and analyzing the display effect, and then put forward several suggestions for the subsequent pixel arrangement design.

P‐124: The IR‐DROP Compensation Method of AMOLED Display under Ultra‐High Brightness

This paper proposes a method to enhance the sunlight readability of AMOLED displays under ultra‐high brightness, and simultaneously improves the global IR‐drop (GIR) issue in light‐loading patterns and the local IR‐drop (LIR) issue in heavy‐loading patterns. In the GIR part, color difference occurs in the brightness increase from high to low APL. Extending to the LIR part, it is found that the uniformity does not exhibit a linear decrease from common brightness to ultra‐high brightness. Finally, based on the approach proposed in this paper, the luminance of OPR 5% is increased to from 1500nits to 3323 nits and color difference is improved from 0.0226 to 0.0012. Besides, the uniformity is enhanced from 61.8% to 86.5% under ultra‐high brightness. Additionally, the proposed improvement compensation method was developed and implemented in driver IC.

P‐6.14: Improvement of Image Sticking Performance in AMOLED Display by Extending Scan Pulse Width via a Novel Driving Circuit

P‐6.14: Improvement of Image Sticking Performance in AMOLED Display by Extending Scan Pulse Width via a Novel Driving Circuit

27‐3: Progress in High‐Performance AMOLED Display with ViP™ Technology

ViP™ (Visionox intelligent Pixelization) Technology is a novel RGB pixelization approach without Fine Metal Mask for OLED patterning. ViP™technology was released in May 2023. In this paper, some key features of display performance and mass production outlook of ViP™ Technology will be discussed.

P‐5.7: Examining Pressure‐sensitive Damping Silicone Adhesive with Excellent Cushioning Capabilities for AMOLED Display

P‐5.7: Examining Pressure‐sensitive Damping Silicone Adhesive with Excellent Cushioning Capabilities for AMOLED Display

Effect of sodium gluconate addition on anomalous codeposition of electroplated nickel-iron alloys

Invar nickel-iron alloy has been widely applied in the fields of electronics, sensors, communications and optics, due to its low thermal expansion coefficient, high hardness, high ductility and other characteristics according to product requirements. The application in metal stencil during the manufacturing process of active-matrix organic light-emitting diodes is mainly due to their good electrical conductivity and soft magnetic properties. In this study, sodium gluconate is used as a substitute for boric acid in the acidic electroplating of nickel-iron alloys; the concentration ratio of nickel-iron in the plating bath is 2:1. After adding sodium gluconate, the precipitation of nickel varies significantly. The iron content in the weight percentage of the deposited nickel-iron alloy is obviously larger than nickel, even up to 3 times. The whole deposition process is in the state of anomalous codeposition, and the selectivity ratio reaches 3 or more; the nickel-iron alloy deposited by adding sodium gluconate to the plating bath has a great influence on the material properties of the nickel-iron alloy plating, The nickel-iron alloy deposited at -1.4 V exhibits a hardness of approximately 3.17 GPa and a modulus of elasticity about 37.88 GPa. Notably, the resistance to plastic deformation of the alloy deposited in sodium gluconate plating solution (H3/U2=0.022) is significantly higher than that in boric acid plating solution (H3/U2=0.007). The experimental results also show that it has the best ability to resist plastic deformation.

Tailoring Subthreshold Swing in A-IGZO Thin-Film Transistors for Amoled Displays: Impact of Conversion Mechanism on Peald Deposition Sequences.

Amorphous IGZO (a-IGZO) thin-film transistors (TFTs) are standard backplane electronics to power active-matrix organic light-emitting diode (AMOLED) televisions due to their high carrier mobility and negligible low leakage characteristics. Despite their advantages, limitations in color depth arise from a steep subthreshold swing (SS) (≤ 0.1 V/decade), necessitating costly external compensation for IGZO transistors. For mid-size mobile applications such as OLED tablets and notebooks, it is important to ensure controllable SS value (≥ 0.3 V/decade). In this study, a conversion mechanism during plasma-enhanced atomic layer deposition (PEALD) is proposed as a feasible route to control the SS. When a pulse of a diethylzinc (DEZn) precursor is exposed to the M2O3 (M = In or Ga) surface layer, partial conversion of the underlying M2O3 to ZnO is predicted on the basis of density function theory calculations. Notably, significant distinctions between In-Ga-Zn (Case I) and In-Zn-Ga (Case II) films are observed: Case II exhibits a lower growth rate and larger Ga/In ratio. Case II TFTs with a-IGZO (subcycle ratio of In:Ga:Zn = 3:1:1) show reasonable SS values (313mV decade-1) and high mobility (µFE) of 29.3cm2 Vs-1 (Case I: 84mV decade-1 and 33.4cm2 Vs-1). The rationale for Case II's reasonable SS values is discussed, attributing it to the plausible formation of In-Zn defects, supported by technology computer-aided design (TCAD) simulations.

A 6T1C pixel circuit compensating for TFT electrical characteristics variations, voltage drop, and OLED degradation

A voltage-programmed pixel circuit based on low-temperature poly-silicon (LTPS) thin-film transistors (TFTs) is presented for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of six p-type transistors and one capacitor (6T1C). During the extraction stage, the circuit extracts the driving TFT’s threshold voltage and the power supply voltage. During the data input stage, the circuit generates a charging voltage, which is associated with the driving TFT’s mobility and the OLED’s threshold voltage. Consequently, the pixel circuit, using only one capacitor, compensates not only for the TFT’s electrical characteristics variations, i.e., the threshold voltage variation and mobility variation, but also for the power supply voltage drop and the OLED degradation. The circuit simulation results reveal that the OLED current error rates (CERs) are lower than 5.09% when the threshold voltage varies by ±0.5V, lower than 3.61% when the mobility varies by ±30%, and lower than 9.16% when the voltage drop varies by −0.5V in the data voltage range.

Recent research on the status and advances of OLED

Organic Light-Emitting Diodes (OLEDs) have already been a prominent display technology in various applications for many decades, ranging from smartphones and televisions to wearable devices and lighting. It is important to understand the current state of OLED research in order to assess its progress, identify challenges, and explore more potential ways for further development. In this paper, the significance and widespread adoption of OLED technology are briefly introduced, and its advantages over traditional display technologies are highlighted. The paper then provides a concise overview of the major components and working principles of OLEDs without delving into basic notions. The paper discusses both small molecule OLEDs (SMOLEDs) and polymer OLEDs (POLEDs), emphasizing their unique structure, characteristics and properties. Different strategies employed to enhance OLED performance is investigated, including the regulation of band gaps that influence the efficiency and brightness. This paper also focuses on the evaluation of device reliability and stability aspects. The techniques and materials employed in studies related to OLED development are also discussed with many searched experimental data and ongoing research activities. Furthermore, the research content covered the aspects of recent commercial advancements in OLED technology, such as Active matrix OLEDs (AMOLED) and Passive matrix (PMOLED). The review provides a guideline for researchers, industry professionals, and enthusiasts to better understand the OLED technology into its details, potential, and the areas that require further exploration.

Nonvolatile Memory Organic Light-Emitting Transistors.

In the field of active-matrix organic light emitting display (AMOLED), large-size and ultra-high-definition AMOLED applications have escalated the demand for the integration density of driver chips. However, as Moore's Law approaches the limit, the traditional technology of improving integration density that relies on scaling down device dimension is facing a huge challenge. Thus, developing a multifunctional and highly integrated device is a promising route for improving the integration density of pixel circuits. Here, a novel nonvolatile memory ferroelectric organic light-emitting transistor (Fe-OLET) device which integrates the switching capability, light-emitting capability and nonvolatile memory function into a single device is reported. The nonvolatile memory function of Fe-OLET is achieved through the remnant polarization property of ferroelectric polymer, enabling the device to maintain light emission at zero gate bias. The reliable nonvolatile memory operations are also demonstrated. The proof-of-concept device optimized through interfacial modification approach exhibits 20 times improved field-effect mobility and five times increased luminance. The integration of nonvolatile memory, switching and light-emitting capabilities within Fe-OLET provides a promising internal-storage-driving paradigm, thus creating a new pathway for deploying storage capacitor-free circuitry to improve the pixel aperture ratio and the integration density of circuits toward the on-chip advanced display applications.