Pixel Shrinkage Research Articles

Efficient electron injection layer for thermal stability of top emission phosphorescent organic light emitting diodes

Thermal stability holds significant importance in both high-resolution and large-area organic light-emitting diodes (OLEDs) due to its potential impacts on pixel shrinkage, thereby adversely affecting visual quality and long-term device functionality. The thermal instability could be from the thermal diffusion of metal ions or small molecules occurring at the interface between the electron injection layer (EIL) and the cathode material, influenced by differing surface properties and binding strength. In this study, we meticulously engineered magnesium fluoride (MgF2) as EIL to mitigate the aforementioned challenges. Important physical properties associated with the EIL/cathode interaction were systematically analyzed. Employing Ag:Yb (2.5:1) as the cathode, we achieved notable enhancements in current efficiency and a reduced turn-on voltage for a green device operating under optical microcavity conditions. Thermal degradation test conducted over 240 h on fabricated devices revealed that employing MgF2 as the EIL markedly enhanced thermal stability compared to devices utilizing Yb as the EIL reference. The robust EIL/cathode system observed herein is attributed to the high binding energy between the EIL and cathode materials utilized in this study.

Human decision-substitutable chemometric identification of pixel shrinkage in OLEDs using secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS)-based depth profiling of organic light-emitting diode (OLED) samples composed of multiple layers is a useful analytical tool for identification of pixel shrinkage, which is a frequent defect occurring in OLED production. As an alternative to engineer-based defect identification, which is time-consuming and occasionally suffers from person-to-person discrepancies, a chemometric analysis scheme utilizing the whole SIMS dataset of the OLED sample has been explored in this study. Initially, all the depth-profiled spectra of each sample were assigned (classified) into the corresponding layers (groups) using a Gaussian mixture model (GMM), and the subsequent average spectra of each layer were used for layer-by-layer comparisons. Then, a one-class support vector machine (OC-SVM) was adopted for defect identification, and principal component (PC) scores of the spectra in each layer were used as the inputs for OC-SVM. The occurrence of defects in the 3rd layer was clear in the PC score domain, and the accuracy obtained by predicting the external test samples was 97.4%. Moving forward, the identification of potential peaks significantly contributing to the defect could be valuable clues to track the causes of defects (trouble shooting) during production. Kernel density estimation (KDE) was adopted for this purpose, and the top nine peaks with the lowest p-values (most significant contributions) were finally provided.

P‐78: An Adhesion Reinforced Structure for TFE of Flexible OLED Display

A design of adhesion reinforced structures was introduced in this study. It was made of negative photoresist and played the role of anti‐peeling. It had a parallel linear shape in the plane and an inverted trapezoidal shape in the section. When bending at 1mm bending radius, the reinforced structure delayed the occurrence of bending failure and limited crack propagation. The promotion of 180°peeling force was over 1000%. Furthermore, it improved pulling force by 16.8% and crush‐resistant by 7.5%. No pixel shrinkage and dark spots appeared when stored in an environment of 85% humidity and at 85 ℃ over 500 hours.

68‐4: A New Thin‐Film Encapsulation Structure for Flexible OLED Display with Long Lifetime

A series of adhesion strength modified layer (ML) was introduced to develop the new TFE structures. The new encapsulation structures provided the long‐life time performance for the flexible OLED device. No pixel shrinkage or dark spots appeared after storing in an environment of 85% humidity and at 85 °C over 20,000 hours. The adhesion strength of the thin film system improved and the risk of peeling decreased.

Degradation of OLED performance by exposure to UV irradiation.

Organic light-emitting diode (OLED) displays are highly susceptible to the harsh environmental conditions found outdoors, like exposure to direct sunlight as well as UV radiation and storage temperature, resulting in a loss of luminance and lifespan, pixel shrinkage, and permanent damage and/or malfunction of the panel. Here, we fabricated top emission OLEDs (TEOLEDs) using Yb : LiF (1 : 1, 2 nm)/Ag : Mg (10 : 1, 16 nm) and Mg : LiF (1 : 1, 2 nm)/Ag : Mg (10 : 1, 16 nm) cathode units and the performances of the devices were investigated by subjecting them to UV radiation. A fabricated red TEOLED (control device), employing a standard Mg : LiF (1 : 1, 2 nm) electron injection layer (EIL) and an Ag : Mg (16 nm) cathode, showed a rapid decrease in luminance and a fast increase in driving voltage at 10 mA cm−2 over time after UV irradiation for 300 h. However, a cathode unit comprising a Yb : LiF (1 : 1, 2 nm) EIL and an Ag : Mg (10 : 1, 16 nm) cathode showed no loss of luminance or increase in driving voltage at 10 mA cm−2 over time after UV irradiation for 300 h. Therefore, we investigated the changes occurring in both cathode units due to UV irradiation using the lift-out FIB-TEM technique and EDS mapping. With UV irradiation for 300 h, Ag atoms migrated toward the center of the cathode, Mg atoms migrated toward the CPL, and no Mg atoms were observed in the EIL area. In contrast, we observed (i) no substantial migration of Ag atoms and they were located at the center of the cathode, (ii) no migration of Mg atoms toward the CPL layer, and (iii) no movement of Yb atoms after UV irradiation. Furthermore, the UV irradiated red TEOLED with an Mg : LiF (1 : 1, 2 nm) EIL showed (i) deterioration in electron injection into the emissive layer (EML) and an increase in the EIL/metal interface resistance, and (ii) a remarkable shift of the J–V curve to the higher voltage side, while almost no such changes were observed in the TEOLD with a Yb : LiF (1 : 1, 2 nm) EIL. Also, an almost identical RGB pixel emitting area was noticed in the Yb : LiF (1 : 1, 2 nm) based devices after UV irradiation for 300 h. These results suggest that Yb could become a good candidate for the cathode unit, providing better device stability against harsh environmental conditions as well as excellent electron injection properties.

OLED Pixel Shrinkage Dependence with Cathode Influenced by Thermal Effect

In OLED displays, pixel shrinkage due to the operating/storage temperature and aging of the devices is causing serious concern. Here, we report an influence of thermally treated Mg:Ag-based thin-film cathode on the OLED pixel shrinkage. The SEM results show significantly pronounced Ag islands formation in only Ag (16 nm) film, annealed at 100 °C for 24 h. On the other hand, a very clean and continuous film is noticed in the Mg:Ag (5:1, 16 nm) cathode before and after the thermal treatments. To address the shrinkage concern, Mg:Ag (10:1, 16 nm), Mg:Ag (1:10, 16 nm), LiF (1 nm)/Mg:Ag (1:10, 16 nm), and Mg:LiF (1:1, 2 nm)/Mg:Ag (1:10, 16 nm) cathodes are fabricated and stored at 85 °C for 240 h. In the Mg:Ag (10:1, 16nm) film, the optical microscope and SEM images reveal the smooth and continuous film. In contrast, the Mg:Ag (1:10, 16 nm) thin film shows islands formation. The surface morphology is significantly improved in the LiF (1 nm)/Mg:Ag (1:10, 16 nm) cathode. Furthermore, a very clean and continuous film is observed when the Mg:Ag (1:10, 16 nm) cathode is deposited on the Mg:LiF (1:1, 2 nm) film. The phosphorescent red TEOLED fabricated using the Mg:LiF (1:1, 2 nm)/Mg:Ag (1:10, 16 nm) cathode shows improved operational performances.

Low-temperature gas-barrier films by atomic layer deposition for encapsulating organic light-emitting diodes

Dependences of gas-barrier performance on the deposition temperature of atomic-layer-deposited (ALD) Al2O3, HfO2, and ZnO films were studied to establish low-temperature ALD processes for encapsulating organic light-emitting diodes (OLEDs). By identifying and controlling the key factors, i.e. using H2O2 as an oxidant, laminating Al2O3 with HfO2 or ZnO layers into AHO or AZO nanolaminates, and extending purge steps, OLED-acceptable gas-barrier performance (water vapor transmission rates ∼ 10−6 g m−2 d−1) was achieved for the first time at a low deposition temperature of 50 °C in a thermal ALD mode. The compatibility of the low-temperature ALD process with OLEDs was confirmed by applying the process to encapsulate different types of OLED devices, which were degradation-free upon encapsulation and showed adequate lifetime during accelerated aging tests (pixel shrinkage <5% after 240 h at 60 °C/90% RH).

Introduction to the Special Issue on Solid-State Sensors

It is my great pleasure to introduce the Seventh Special Issue of the IEEE TRANSACTIONS ON ELECTRON DEVICES on Solid-State Image Sensors. Previous special issues were published in February 1976, August 1985, May 1991, October 1997, January 2003, and November 2009. During the six-year interval since the last special issue, significant changes have occurred in the field of solid-state image sensors. This is due, in particular, to the drive for low-power, high integration, compact imaging systems. Now that the speed of pixel shrinkage is slowing down, various new technologies are being developed to increase the functionality of the sensors, to make them more compact, to make them faster, to increase their dynamic range, etc. Papers reflecting these trends in the image sensor technology are well represented in this special issue.

P‐159: Protecting Large Area OLED Displays from Dead Pixels Caused by Lid Deflection

AbstractDuPont has developed a UV curable acrylic material that can be used as a fill material for large area OLED displays to eliminate dead pixels caused by cover lid deflection, without causing pixel shrinkage or OLED degradation after 1,000 hours of testing at 85 °C and 60 °C/ 90% RH.

P-235L: Late-News Poster: Analysis of the Relationship Between OLED Performance and Dryer Characterization

The successful exploitation of OLED/PLED displays is dependent on the control and removal of moisture from the device. Pixel shrinkage and luminosity reduction during the operating conditions are the most relevant issues, related to the moisture concentration into the device. Results show a strong link with dryer absorbing speed more than total capacity, as forecasted by a suitable model.

CMOS-Based Image Sensors

CMOS-based image sensors have recently emerged as strongest counterparts to CCDs (Charge Coupled Devices) thanks to great improvements in image quality. The CMOS-based image sensors are generally featured by (1) fast parallel readout, (2) low power consumption and (3) on-chip peripheral circuit capability. Also, for D-SLR (Digital-Single Lens Reflex) cameras, &#x201C;stitching technology&#x201D; allows only CMOS-based image sensors to provide practical 35mm-format imagers. The CMOS-based image sensors are starting to contend with CCDs in small pixels such as less than 3um. Different pixel shrinkage schemes have been proposed along with process design rule miniaturization. Market demands and intense competition will continue to be the main factors to drive the technologies of CMOS-based image sensors.

Polyimide Coatings for OLED Applications

We developed novel positive-tone photosensitive polyimide coatings for insulation layers in organic light emitting diode (OLED) displays. We evaluated the features of the novel coatings in comparison to other candidate polymers including novolak resin, acrylic resin, and polybenzoxazole. After curing, the novel coatings exhibited excellent and stable electrical and thermal properties, and good adhesion to various substrates with quite a low thickness loss during cleaning process, e.g., UV-O3, O2-plasma, etc. In addition we confirmed that the novel coatings could solve the pixel shrinkage problem in OLED displays.

Novel patterning method using Nd:YAG and Nd:YVO 4 lasers for organic light emitting diodes

A laser ablation method has been applied to the patterning of the cathode of organic light emitting diodes (OLEDs). Second harmonic (532 nm) from the diode pumped by solid state Nd:YAG and Nd:YVO 4 lasers were used. The devices fabricated show the similar characteristics those made by using cathode separators. By using the “laser patterning method”, one step of photolithography process that required to making barrier rib can be removed. And this technique has less possibility of contamination of ITO/organic interface and superiority in the view point of pixel shrinkage, so that longer lifetime of device is expected.