Materials Used in Electroluminescent Displays
- PDF / 3,718,175 Bytes
- 10 Pages / 576 x 777.6 pts Page_size
- 78 Downloads / 196 Views
rials Used in Electroluminescent Displays P.D. Rack, A. Naman, P.H. Holloway, S-S. Sun, and R.T. Tuenge Introduction The flat-panel-display (FPD) market is experiencing rapid growth due to increased demand for portable computers, communication equipment, and consumer electronic products. In all of these applications, the display is the primary human interface that conveys information. The size of the flat-panel-display market is presently estimated to be $10 billion/year and is projected to grow to over $18 billion/year by 1998. Although most current FPDs utilize either passive- or active-matrix liquid-crystaldisplay (LCD) technology, electroluminescent (EL) displays and light sources, because of their solid-state construction and self-emissive characteristics, can provide improved performance for many demanding display applications. Thinfilm electroluminescent (TFEL) technology has been demonstrated over a broad range of display sizes from 1-in. to 18-in. diagonal with resolutions from 50 to 1,000 lines per inch. Also, because of its unique solid-state characteristic, TFEL technology is well-suited to provide a fully integrated display with the lightemitting element and electronics fabricated on the same substrate. An example of a full-color TFEL display is shown in Figure 1. Thin-film electroluminescent display panels are finding increasing applications in the FPD marketplace due to several fundamental performance advantages over LCDs. These include wide viewing angle, high contrast, wide operating-temperature range, ruggedness, and long lifetime. Alternating-current (ac)-driven monochrome TFEL displays (ACTFEL displays) have become the most reliable, longest running devices on the market. Commercial ACTFEL display panels have operated for more than
MRS BULLETIN/MARCH 1996
Figure 1. Full-color alternating-current thin-film electroluminescent (ACTFEL) display from Planar Systems.
49
Materials Used in Electroluminescent Displays
Insulator
Electroluminescent Phosphor Insulator Figure 2. Schematic representation of the four steps necessary to produce electroluminescence. In step 1, electrons tunnel from electronic states at the insulator/phosphor interface. In step 2, electrons are accelerated to ballistic energies by high fields in the phosphor. In step 3, the energetic electrons impact-ionize the luminescent center or create electron-hole pairs that lead to activation of the luminescent center. In step 4, the luminescent center relaxes toward the ground state and emits a photon.
Lamp technology generally does not use thin films because of cost but instead uses powders in thick-film inks as described in the section on Thick-Film Electroluminescent Lamps. This market is also expanding and many of the advantages cited for the ACTFEL displays are also true for powder thick-film EL lamps. Historical Perspective Electroluminescence (EL) is a phenomenon that converts electrical energy to luminous energy without thermalenergy generation. Observations of the electroluminescence phenomenon date back to the 1920s.1 Impo
Data Loading...
