Tariq A. Ali

29.4L: Late-News Paper: Dual Doped High Tg White Organic Light Emitting Devices on Silicon

We report the fabrication of efficient surface-emitting white organic light emitting diodes (OLEDs) on single crystal silicon substrates using a high Tg blue host layer with co-deposited blue-green and red-orange emitter dopant molecules. The emission layer is sandwiched between a Spiro-TAD hole transport layer and an Alq3 electron transport layer. The devices operate near the 1931 CIE white balance point with luminous efficiencies of 2.75 lum/W and current efficiencies of 8 cd/A, representing luminance of ∼1600 cd/m2 at a current density of 20 mA/cm2. When tested under accelerated and uninterrupted 90% pulsed 20 mA/cm2 drive, our OLEDs yield luminance half-lives of over 5000 hours, which represent normalized half life at 100 cd/m2 for color microdisplays of greater than 20,000 hours assuming a 25% duty cycle similar to that created by full motion video. These results enable us to meet commercial and military requirements for OLED color microdisplays employing passband filters for red, green and blue subpixel elements.

Structure and characterization of a white up-emitting OLED on silicon for microdisplays

We have developed highly efficient, top-emitting white OLED structures suitable for black-and-white or full color microdisplay applications. White light emission was obtained from both singly doped and doubly doped emitter layer structures. However, the double-dopant structure, employing fluorescent blue and red-emitting dyes, generated much higher luminous efficiency than that of the single dopant structure incorporating only the red dopant. For top- emitting, white OLED devices with the double-dopant structure, we have achieved luminous efficiencies of 974 cd/m2, 4.9 cd/A, 1.9 lm/W and an external quantum efficiency of 1.8% when driven at 20 mA/cm2 and 7.9 V. The device has an electroluminescence turn-on voltage of 2.2 V. After turn-on, the current varies as the 14th power of the voltage. The projected operational half-life of these devices is greater than 6000 hrs. This estimate is based on devices that have been continuously driven at a constant current of 20 mA/cm2 for more than 3000 hrs. Based on an up-emitting, double-dopant white OLED structure, we have developed an SXGA-resolution, black-and-white active matrix OLED (AMOLED) on silicon microdisplay. This AMOLED-on-Si has demonstrated real-time video with 256 gray levels and consumes less than 400 mW of power at a brightness of 200 cd/m2.

Recent advances in small molecule OLED-on-silicon microdisplays

High resolution OLED-on-silicon microdisplay technology is unique and challenging since it requires very small subpixel dimensions (~ 2-5 microns). eMagins OLED microdisplay is based on white top emitter architecture using small molecule organic materials. The devices are fabricated using high Tg materials. The devices are hermetically sealed with vacuum deposited thin film layers. LCD-type color filters are patterned using photolithography methods to generate primary R, G, B colors. Results of recent improvements in the OLED-on-silicon microdisplay technology, with emphasis on efficiencies, lifetimes, grey scale and CIE color coordinates for SVGA and SXGA resolution microdisplays is presented.

53.3: High Performance Top Emitting Green OLED Micro‐Displays

Efficient top-emitting phosphorescent green OLED micro-displays were developed using a highly reflective anode patterned over active matrix single crystal silicon. Single emission layer devices were fabricated using high Tg materials with efficiencies ∼80 cd/A, 18% EQE and stable green color coordinates (0.33, 64). Green OLED Micro-display lifetimes were measured.

59.2: High Performance Top Emitting OLED Devices

High performance top-emitting full color organic light-emitting diode (OLED) micro-displays were developed using a highly reflective anode patterned over active matrix single crystal silicon. Dual emission layer white OLED devices were fabricated using high Tg materials with typical efficiencies ∼ 10 cd/A and CIE x and y coordinates of 0.32 and 0.34 respectively. Stable color coordinates over a wide range of video grey levels were obtained from white using color filters. Room temperature operating luminance half-life at 20 mA/cm2 exceeds 6,000 hrs (>25,000 hrs in video mode). The optical characteristics of the devices were simulated using a full vector field calculation.

Technology and design of an active-matrix OLED on crystalline silicon direct-view display for a wristwatch computer

The IBM Research Division and eMagin Corp. jointly have developed a low-power VGA direct view active matrix OLED display, fabricated on a crystalline silicon CMOS chip. The display is incorporated in IBM prototype wristwatch computers running the Linus operating system. IBM designed the silicon chip and eMagin developed the organic stack and performed the back-end-of line processing and packaging. Each pixel is driven by a constant current source controlled by a CMOS RAM cell, and the display receives its data from the processor memory bus. This paper describes the OLED technology and packaging, and outlines the design of the pixel and display electronics and the processor interface. Experimental results are presented.

P‐150: High Temperature High Performance Top Emitting Yellow OLED

Efficient top-emitting phosphorescent yellow OLED micro-displays were developed on active matrix single crystal silicon. Very stable 1931-CIE coordinates across a wide range of current density were achieved in single emission zone devices with efficiencies ∼55 cd/A, 18% EQE relative to dual emission zone devices. Device lifetimes were measured.

P-153: Exciton Distribution and Microcavity Effects in Designing Top Emitting OLED Devices

Micro-cavity and exciton distribution are investigated in top-emitting organic light-emitting diode (OLED) devices having a highly reflective anode patterned over silicon wafers. A narrow (delta-doped) sensing layer method was used to obtain the exciton distribution profile for various dopant combinations using a single or a double emissive layer. Results are compared to OLED with lower reflectivity anode. The exciton diffusion length plays a critical role in tuning the color coordinates of the emitted light when multiple emission layers are used in combination with microcavity to achieve a white top emitter OLED.

OLED microdisplay design and materials

AMOLED microdisplays from eMagin Corporation are finding growing acceptance within the military display market as a result of their excellent power efficiency, wide operating temperature range, small size and weight, good system flexibility, and ease of use. The latest designs have also demonstrated improved optical performance including better uniformity, contrast, MTF, and color gamut. eMagins largest format display is currently the SXGA design, which includes features such as a 30-bit wide RGB digital interface, automatic luminance regulation from -45 to +70°C, variable gamma control, and a dynamic range exceeding 50:000 to 1. This paper will highlight the benefits of eMagins latest microdisplay designs and review the roadmap for next generation devices. The ongoing development of reduced size pixels and larger format displays (up to WUXGA) as well as new OLED device architecture (e.g. high-brightness yellow) will be discussed. Approaches being explored for improved performance in next generation designs such as lowpower serial interfaces, high frame rate operation, and new operational modes for reduction of motion artifacts will also be described. These developments should continue to enhance the appeal of AMOLED microdisplays for a broad spectrum of near-to-the-eye applications such as night vision, simulation and training, situational awareness, augmented reality, medical imaging, and mobile video entertainment and gaming.