Webster E. Howard

Microdisplays based upon organic light-emitting diodes

Microdisplays, some of which exploit the dense electronic circuitry in a silicon chip, are enabling a new wave of ultraportable information products, including headsets for viewing movies and cell phones with full-screen Internet access. This paper reports the approach to microdisplay development at eMagin Corporation. The requirements for microdisplays are reviewed, and the case is made that organic light-emitting diodes (OLEDs) are the best candidate transducer technology for meeting these requirements. A 1280 × 1024 (SXGA) monochrome OLED microdisplay is described as an example.

High-resolution color organic light-emitting diode microdisplay fabrication method

We report experimental results on the evaluation of a sealing technique for organic light emitting diodes (OLEDs) used for high-resolution color microdisplay applications. Based on production and processing requirements for active matrix OLEDs (AMOLEDs) on silicon, the sealing process must protect the device against moisture and oxygen, not only during operation and storage but also during production. A conformal polymer/metal(oxide)/polymer multi-layer technology was selected for this purpose. AMOLED test structures were produced and tested with and without sealing under ambient conditions as well as in water. The applied sealing process was shown to be compatible with all steps of the OLED-based microdisplay production of eMagin Corporation. Our results confirm that encapsulating AMOLEDs with the described process leads to increased stability, both under operation as well as for storage purposes.

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.

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.

VGA active-matrix OLED displays having the single polysilicon TFT pixel structure

Organic light emitting diodes are a new flat panel display technology that offers high luminous efficiencies. In this paper, a VGA format polysilicon active matrix organic light emitting diode display will be presented. The display design and pixel structure will be discussed as well as the integration of the polysilicon TFT with the OLED display process. The method used to drive the display will be presented along with the active matrix display performance.

Design and manufacturing of active-matrix organic light-emitting microdisplays on silicon

An organic light-emitting diode (OLED) microdisplay is described. The OLED display has a top-emitting structure integrated on single-crystal active-matrix driver chips and is sealed in a fully hermetic package. All processing and fabrication is done on 8-in. wafers until final dicing and assembly. The basic structure of the displays, the key manufacturing and processing steps, and initial performance of a monochrome green active-matrix OLED device structure are presented. Key advantages of the chosen approach as well as remaining challenges and requirements for improvements are discussed.