Overview of FLCOS Technology

All of Micron's microdisplays are are built with ferroelectric liquid crystal on silicon (FLCOS) technology. The key distinction between FLCOS and the more common type of liquid crystal on silicon (LCOS)—nematic liquid crystal (NLC)—is speed. Our Displaytech FLCOS technology switches up to 100 times faster than standard Nematic LCOS. The speed of the FLCOS allows a single FLCOS panel to display a full color image.

Our Displaytech FLCOS microdisplays combine fast, small, digital liquid crystal technology with integrated circuit backplanes, putting the liquid crystals directly on top of the backplane. The binary nature of our ferroelectric liquid crystals (FLC) matches perfectly with these digital backplanes to provide a fully digital microdisplay that uses less power than other microdisplays. They can also operate in much colder temperatures. Other microdisplays use nematic liquid crystals that are inherently analog, requiring more complex liquid crystal drive schemes.

How it Works

Each pixel in an FLCOS device is at all times in one of only two states (ON or 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 (see the Digital Grayscale images below).

The FLCOS panel displays color using a technique referred to as field sequential color (FSC). In FSC, the color of the light illuminating the entire panel is cycled from red to green to blue. This is done so rapidly that the human eye integrates the three colors sequentially to percieve full color for each individual pixel. In contrast, nematic displays achieve color on each pixel by spatially dividing it into three "sub-pixels." Each sub-pixel is 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 perceive full color. The FLCOS image comparison illustrates the difference in image quality between these two methods.

Technical Details – How FLCOS Switching Happens

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.

FLCOS Image Comparison

Digital Gray Scale

Sequential Color—1 Frame

Digital Gray-scale Image Processing