The multi-billion-dollar display market has grown to encompass everything from notebook PCs to desktop monitors, televisions, cell phone displays, and much more. As the market continues to evolve, product designers struggle to differentiate their products by adding more capability to current products and by introducing a range of new products. One significant challenge facing designers is how to incorporate a display that is truly “watchable” as high-quality video content is displayed. To overcome this problem, designers are turning to newer display technologies like ferroelectric-liquid- crystal-on-silicon (FLCOS) technology.
FLCOS displays have been used in over 14 million shipped video camcorders and digital still cameras, illustrating the maturity of the technology and that it is well suited to help consumer electronics companies meet this emerging challenge. FLCOS displays enable unsurpassed image resolution, power efficiency, and ease of manufacturability, and are designed to be versatile enough to project video for a wide range of devices.
FLCOS and Microdisplays
The key difference between FLCOS and competitive microdisplays is its use of ferroelectric liquid crystals (FLCs). FLCs switch at incredibly high speeds of less than 100 μsec, while conventional nematic liquid crystals are only capable of switching in the 10 msec range. The FLCOS display sandwiches the FLC between a piece of glass and a pixelated reflective CMOS die. The CMOS circuitry accepts standard video signals and converts the signals into digital voltages that are independently applied to each of the aluminum pixel mirrors. The pixels then create a field across the FLC and, depending on the direction of the field on each pixel, the polarized light passing through the FLC and reflected off the pixelated mirrors is either rotated or not rotated. Since only one polarization is sent to the viewer’s eye, each individual pixel is controlled by the silicon.
The reflective pixels on the CMOS die are formed using the top metal layer of the 0.25-μm silicon process, allowing very high fill factors and optimized pixel geometries. In our QVGA display, we implemented offset hexagonal pixels, making the image appear to have resolutions like competitive VGA displays.
There are other significant advantages of incorporating VLSI circuitry into our FLCOS display, such as integrated dual frame buffers, active temperature compensation, true gamma control, and LED timing controls, all without the requirement of additional electronic components. The FLCOS microdisplay, using the fast speed of the FLC, creates 8 bits of gray scale (per color) with true pulse width modulation, and generates a high frame rate sequence of red, green, and blue (RGB) images. The human eye integrates the sequence into full-color images.
The FLCOS microdisplays are a proven technology that provides versatile solutions to solve a number of the roadblocks engineers now face in developing the next generation of consumer electronics. One important aspect of being CMOS-based is that FLCOS displays can take advantage of high-volume VLSI interconnect and packaging technologies that are inherently consistent with small size, low power, and consumer pricing models.
Newly introduced FLCOS displays offer higher resolutions including VGA, WVGA, and SVGA. These products are offered to fill the need for small, high-resolution microdisplays that is being driven by the marketplace for personal communication devices, head-mounted displays, and small projectors. These new FLCOS panels require less than 100 mW and support a standard RGB video interface. When illuminated with announced RGB LEDs, these new panels should be capable of projecting an image of 100 lumens. The packaged size of FLCOS microdisplays is less than a half-inch in height, allowing them to be embedded easily into most personal electronic devices or to create stand- alone projectors that can be attached easily to a range of portable devices. The high-resolution panels also can be applied in near-to-eye applications such as high-end electronic viewfinders and head-mounted displays.
FLCOS technology is also applicable in non-display products. For example, the FLCOS spatial light modulator (SLM) offers the high switching speed and optical throughput necessary to effectively switch the deep-blue laser light used in holographic data storage devices. In holographic data storage applications, the FLCOS technology encodes information onto the data-carrying laser beam that is written into the holographic medium. The SLM maps the electronic data of 0s and 1s into an optical “checkerboard” pattern of more than one million light and dark pixels. This allows data to be recorded volumetrically in the recording medium — not just on the surface of the disc, as is the case with current DVD technologies.
FLCOS is uniquely suited to help consumer electronics companies meet increased functionality required for next-generation devices. Already proven as electronic viewfinders in digital cameras and video camcorders in consumer markets, FLCOS is beginning to enable a number of new display and non-display applications across many different markets.
This article was written by Bruce Spenner, Executive Vice President of Displaytech, Inc., Longmont, CO. For more information, Click Here