Overview of FLCOS—How it works

The bottom line (at the top!)

All of Displaytech's liquid crystal devices are built with Ferroelectric Liquid Crystal (FLC) designed & manufactured in our facility in Longmont, Colorado. The key distinction between FLC and the more common type of liquid crystal, called Nematic Liquid Crystal (NLC) is speed. FLCOS switches up to 100 times faster than standard Nematic liquid crystal. The speed of the FLCOS allows a single FLCOS panel to display a full color image.

"Displaytech combines fast, small, digital liquid crystal technology with integrated circuit backplanes, putting FLCs directly on top of the backplane. The binary nature of FLCs matches perfectly with these digital backplanes to provide a fully digital microdisplay that switches ten to one hundred times faster and at lower voltages than other microdisplays. Other microdisplays use nematic liquid crystals that are inherently analog, requiring more complex liquid crystal drive schemes." —Mark Handschy, Chief Scientist, Displaytech

Technically speaking

The FLC layer inside an FLCOS device is optically anisotropic and behaves as a uniaxial medium with its optic axis in the plane of the layer. When an electric field is applied, the optic axis assumes a uniform direction throughout the layer. When the polarity of the electric field is reversed, the optic axis rotates 45°. This gives the cell exactly two stable states that are determined by the polarity of the applied electric field. By selecting the appropriate thickness of the FLC layer (i.e., where retardance is one-half of the operating wavelength), it functions as an electrically switchable half wave plate.

Layman's terms

Each pixel in an FLCOS device is at all times in one of only two states (ON and OFF) and switches between those two states in about a hundred microseconds. To make a display the FLCOS device must modulate light intensity and color. To accomplish this FLCOS devices generate grayscale or light intensity using Pulse Width Modulation (PWM). The pulse width defining when a pixel is on is controlled by the electronics to one part in 256 thus achieving 8 bits of grayscale. The Digital Grayscale images below show this pictorially. The FLCOS panel displays color using a technique referred to as field Sequential Color (FSC). Using this technique the color of the light illuminating the entire panel is cycled from red to green and then to blue. This is done very rapidly so the human eye integrates the three colors sequentially to see full color on each individual pixel. In contrast, nematic displays achieve color on each pixel by spatially dividing it into 3 "sub-pixels" with each sub-pixel being entirely covered by either a red, green, or blue filter. These are placed very close together so the human eye integrates the three colors spatially to see full color. The FLCOS Image Comparison illustrates the difference in image quality between these two methods.

FLCOS Image Comparison

Digital Gray Scale

Sequential Color—1 Frame

Digital Gray-scale Image Processing