Like FEDs (field emission displays), EL (electroluminescent) displays are emissive devices. Instead of modulating a backlight, as LCDs do, EL displays produce their own light by applying voltage to a phosphor. The advantages of EL displays include their rugged construction, ability to operate in an extended temperature range, and low power consumption. In addition, EL displays are the only ones that are completely solid-state.
Working with a team that includes Kopin and the David Sarnoff Research Center, Planar America is currently developing an AMEL (active-matrix electroluminescent) display. Each pixel site on this display has its own transistor, an approach that seeks to achieve the same advantages as Kopin's single-crystal LCD proce
ss (see the main text for details about this process). All the drive electronics and pixel transistors are fabricated in a modified silicon foundry. Phosphors are then deposited directly onto these electronics.
"AMEL fabrication requires only a single substrate," explains Ron Khormaei of Planar America. "This eliminates the assembly and alignment of two substrates, which is required for all other flat-panel technologies."
AMELs may be well suited to HMDs (head-mounted displays) and portable-computing devices that require screens with low power consumption and extended operating-temperature ranges. That's why the military is interested in this technology. In fact, the U.S. Army is making preparations to flight-test an AMEL-based HMD next winter.
Development is still in its early stages, however, and moving from prototypes to volume manufacturing will take time and money. Planar recently received a $29 million contract to develop manufacturing processes that will allow pilot production of A
MEL screens. The company hopes to begin sampling monochrome VGA displays and 640- by 512-pixel color displays by next summer.
Developing a bright and stable blue phosphor has long been an elusive goal for Planar. However, the company recently announced a breakthrough in this area. While the first samples are targeted primarily for high-performance military devices, Planar is also eyeing opportunities for HMDs and other applications.
EL DISPLAY ADVANTAGES
-- rugged construction
-- ability to operate in an extended temperature range
-- low power consumption
-- only completely solid-state displays
Active-Matrix EL Displays
