Browse Prior Art Database

Vertical-Cavity Organic Light-Emitting Diode Display

IP.com Disclosure Number: IPCOM000118954D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 118K

Publishing Venue

IBM

Related People

Riess, W: AUTHOR [+3]

Abstract

Disclosed is a device comprising of an array of Organic Light-Emitting Diodes (OLEDs) on an opaque substrate in which the emitted color is selected using vertical optical cavities. By laterally varying the thickness of the Vertical Cavity (VC), adjacent regions of an otherwise identical OLED array can be made to emit different wavelengths of light due to interference and cavity effects. In this way, a full color display on an opaque substrate can be fabricated with a uniform, blanket organic layer structure.

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Vertical-Cavity Organic Light-Emitting Diode Display

      Disclosed is a device comprising of an array of Organic
Light-Emitting Diodes (OLEDs) on an opaque substrate in which the
emitted color is selected using vertical optical cavities.  By
laterally varying  the thickness of the Vertical Cavity (VC),
adjacent regions of an otherwise identical OLED array can be made to
emit different wavelengths  of light due to interference and cavity
effects.  In this way, a full color display on an opaque substrate
can be fabricated with a uniform,  blanket organic layer structure.

      Obtaining full color from OLED-based displays is still
problematic, but VCs have emerged as one viable solution (1).  A VC
is an optical cavity formed by two parallel mirrors, one of which is
nearly 100% reflecting and the other of which is only partially
reflecting.  Light is extracted from the device through the latter
mirror.  As applied to OLEDs, the high reflectivity mirror is
typically one of the metal contacts, and the partial mirror is a
Distributed Bragg Reflector (DBR) composed of a multi-layer stack of
materials with alternating high and low indices of refraction.

      For this scheme to be successfully applied to fabrication of
color displays, several parameters must be balanced (2).  The VC must
be sufficiently thin that its modes are spaced more widely than the
largest spacing between the wavelengths that one wishes to extract.
For a full color display, for example, extraction at peak wavelengths
of 435, 520, and 635 nm light might be desired.  The VC mode spacings
(or free spectral range) must, therefore, be > 220 nm, so blue and
red light  do not radiate simultaneously.  Furthermore, the VC
mirrors must be designed to reflect efficiently over the entire
wavelength range of interest.  For the previous example, a mirror
stopband of > 200 nm is needed.  This can be achieved with a metallic
mirror on one side and a  DBR with a high refractive index contrast
on the other.  Finally, the OLED must have broadband emission
(excluding VC effects) so that it is  capable of radiating at each of
the desired wavelengths under the influence of the VC.

      In this invention, a method is provided for integrating a
VC-modulated OLED array with an opaque substrate, preferably one
containing circuitry, for example, active-matrix pixel and drive
circuitry, for controlling the OLEDs.  The opaque substrate dictates
that the light be extracted through the OLED top contacts and the DBR
mirror.

      One preferred VC OLED display embodiment is shown in the
Figure.  In this approach, the organic layers and transparent top
contact are deposited directly onto a silicon wafer containing
integrated circuitry and are capped by...