Electronic Design

Ferroelectric Microdisplays Enlist In A New Defense Application

A reflective, ferroelectric LCD microdisplay will play a major role in a pair of simulator optics subsystems in the latest version of the Starstreak Self-Propelled Air Defence Weapon System, used by the British Army. The first of these subsystems is a simulated binocular sighting device. The second is a monocular sighting device that uses a different field of view than the binocular unit.

In both of these subsystems, light from the LED illuminator travels through the polarizing beamsplitter (PBS) to the 1024- by 768-pixel LCD microdisplay. It is then reflected back through the PBS and projected through the viewer eyepiece (see the figure).

Ferroelectric microdisplay fabrication depends on the application of a very thin layer of ferroelectric material—less than 1 µm—on top of the silicon die. Pixel size is governed by the liquid-crystal thickness. Ferroelectric technology, then, is beneficial because it provides a liquid-crystal bandgap that enhances the display's switching speed and tightens the interpixel gaps, enabling very small pixels.

Pixel pitch is typically 5 to 6 µm. (A human hair is 70-µm thick.) Ferroelectric microdisplays can switch at 100 µs, which is far faster than conventional LCDs. Consequently, frame rates can be quite high. Also, power consumption is unusually low.

For a given pitch, ferroelectric microdisplay manufacturers can use the smallest dies. Or for a given die size, they can place more pixels on the die than anyone else. In other words, ferroelectric microdisplay manufacturers say they can produce the smallest die for a given resolution.

Other applications for ferroelectric microdisplays in defense include simulated laser range finders, missile trainers, and night-vision systems. In consumer applications, ferroelectric LCDs are well suited for viewfinders, head-mounted displays, PDAs, communicating wristwatches, and wireless Internet devices.

The Starstreak system was developed by Shorts Missile Systems Ltd., Belfast, Northern Ireland. Its microdisplay devices will be supplied by two English firms, CRL Opto of Hayes, Middlesex, and Davin Optronics Ltd. of Borehamwood, Hertfordshire.

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