There is an emerging opportunity to integrate high quality video displays into small, pocket-sized communication devices like cell phones. The proliferation of easily accessible video content on wired and wireless networks has captured the attention of network service providers because of the opportunity to sell video services to end users. The product design challenge is to provide a display that is sized for comfortable viewing while maintaining the pocket size of the communication device. This article describes how ferroelectric-liquid-crystal-on-silicon (FLCOS) microdisplays have come to the forefront as the display technology capable of solving the dilemma of creating an acceptable video display from an extremely small package.
How FLCOS works
The twenty-five year old FLCOS microdisplay technology is today found in over 14-million shipped products. Now. it is positioned to enable consumers to comfortably view video images in a variety of new applications, including portable projectors, automotive displays, and near-to-eye displays. They can also be used for holographic data storage.
FLCOS microdisplays are differentiated from other microdisplays by their use of proprietary ferroelectric liquid crystals (FLC) which switch in under 100usec, as compared to conventional nematic liquid crystals which switch in the 10msec range. This fast switching speed enables a single complementary metal-oxide-semiconductor (CMOS) silicon die whose surface is coated with FLC to produce full color displays. The CMOS circuitry interfaces to a standard video input and creates the image on the pixilated reflective mirrors that are implemented using the top layer of metal from the CMOS process. The FLC material interacts with the light passing through the material either rotating or not rotating the polarization of the light based on the voltage placed on the pixilated metal by the CMOS circuitry. The FLCOS microdisplay uses the fast speed of the FLC to generate a high frame rate sequence of red, green and blue (RGB) images which the human eye integrates into full-color images. Because the FLCOS microdisplay is CMOS-based, it can use high-volume interconnect and packaging technologies that are inherently consistent with small size, low power and consumer pricing models.
Figure 1: FLCOS microdisplays
The FLCOS microdisplay provides a versatile solution to a number of roadblocks engineers now face in developing the next generation of consumer electronics that are targeted to provide consumers with comfortably viewable video images. A next generation of FLCOS microdisplays is uniquely suited for high-resolution personal display products, including head-mounted displays and ultra-small, full color projectors. These new FLCOS products are an outgrowth of the learning gained by the high volume production of QVGA electronic viewfinders, which matured both the manufacturing processes and product design.
FLCOS microdisplays will now be offered in higher resolution VGA, WVGA, and SVGA versions. The three new FLCOS panels have active area diagonals from 0.4″ to 0.5″, require less than 100mW and support an RGB video interface. When illuminated with announced RGB LEDs, these new panels will allow a projected image of 100 lumens, enabling a number of next-generation consumer electronics, including embedded and standalone projection devices and automotive display applications. The high-resolution panels can also be applied in near-to-eye applications such as high-end electronic viewfinders and head-mounted displays.
Next: Embedded projection devices
Embedded projection devices
Personal mobile electronic devices that incorporate projection capability are referred to as embedded projection devices. These devices place tight constraints on the projection components, size, power dissipation and cost. The overall flexibility of FLCOS microdisplays provides designers with a unique opportunity to bring embedded-projection solutions to the next-generation of personal mobile devices. The FLCOS panel provides the display and the display controller, includes the control signals for the LED, and dissipates less than 100 mW. With a standard RGB video interface designed into the FLCOS microdisplay, engineers can focus their attention on the critical task of minimizing the power used by the projection light source.
The size of FLCOS microdisplays is also critical for embedding projectors into personal devices like cell phones, PDAs and media players. The packaged size of FLCOS microdisplays is less than a half-inch in height, allowing them to be easily integrated into most personal devices. Because the FLCOS device incorporates a standard video interface, no additional interface components are required, thereby minimizing the space required to embed the projector.
Although the new FLCOS microdisplays do not completely remove all the challenges associated with embedding a projector in a personal device, they do make it possible because of the unique characteristics of FLCOS devices.
Figure 2: The Displaytech LV311
Standalone personal projection devices
Standalone personal projection devices are designed to be attached to other personal electronic devices. At the approximate size of the average PDA, these hand-held personal projectors must deliver high-resolution projected images for business and entertainment but still fit easily into your pocket. Some of the same concerns associated with embedded projection are, therefore, associated with standalone projection devices: size, weight, power, and standard interface. In order to be desirable to most consumers the device must be lightweight and stingy with power to allow the projector to operate on battery for a reasonable time period. Standalone devices can also utilize a power cord to extend the time the projector will operate. Information can be fed to the projector either via a wire or wirelessly, or using a form of portable memory.
The size and weight of the microdisplay is well-engineered for small devices and the low power required makes the FLCOS solution desirable in a portable, battery-operated projector. Fast switching speeds offered by FLCOS microdisplays means a single display panel will produce full color and the >90% aperture of the reflective FLCOS generates a high quality projected image.
Next: Near-to-eye applications
FLCOS microdisplays have been applied as electronic viewfinders in both digital still cameras and video camcorders. FLCOS has been shipping in this application for the past 6 years, with over 14-million FLCOS microdisplays shipped for use as electronic viewfinders in digital still and video cameras offered by the world's leading electronics manufacturers.
FLCOS microdisplays are being applied in other near-to-eye applications, for example, in head-mounted displays. In both near-to-eye applications the illumination source is tri-color LEDs that are controlled by the electronics integrated into the display panel. The LED light source has proven to supply more than enough light for the near-to-eye applications when coupled with FLCOS microdisplays.
One absolute requirement for a near-to-eye display is that the display generates full color using a single panel. Only FLCOS panels with their very fast switching speed are capable of the very high frame rates necessary to make a sequential color display. All competitors' panels use color triads to generate full color using a single panel. The small aperture of the color triad panels lead to near-to-eye displays that look like you are looking at the image through a screen door. The FLCOS reflective display using sequential color creates the intended color over the entire >90% aperture of each pixel thereby producing a photograph-like image.
An additional consideration when selecting a display is the color gamut provide by the display. Competitive near-to-eye displays form their color triads using color filters that produce a very limited color gamut. The FLCOS panels use tri-color LEDs that generate a wider color gamut, producing color that is more true-to-life.
The complicated nature of designing a successful near-to-eye display has been simplified with FLCOS microdisplays. FLCOS provides a high-quality full-color image on a single microdisplay, without the need of color dyes. Because of their small size and functionality, such microdisplays are flexible enough to help engineers design an attractive near-to-eye application.
Automotive applications are another space in which FLCOS technology could prove disruptive. Automotive display monitors are increasing by double-digit rates and are forecast to continue to do so until 2010, according to DisplaySearch, a display industry analysis firm. Multi-function global positioning system (GPS) technology and driver information displays are spreading across the dashboard in more and more automobiles, and entertainment-oriented displays are showing up mounted to ceilings and the back of headrests in many new vehicle designs. In addition, heads-up displays that project information directly in the driver's line of sight using the windshield itself as a projection surface are also becoming increasingly attractive to automakers seeking to stand out in a crowded automotive marketplace.
Microprojection is a new technology for automotive applications. Any time an automobile picks up a new technology, there is a period of testing and validation which will include the use of the new technology in non-critical areas like entertainment displays.
One of the challenges designers face with displays located in automobiles is maintaining good display contrast in high ambient light situations. Ambient sunlight hitting any display causes the image to appear washed out. FLCOS microdisplays don't directly solve this problem but the use of a projection system gives the designer new alternatives. Advances in projection screen technology are making available screens with the capability to reject ambient light and thereby improving the display contrast in high ambient light situations.
Next: Holographic data storage
Holographic data storage
Holographic data storage (HDS) is an example of non-display application that FLCOS is enabling. In the HDS application space, the FLCOS device is referred to as a spatial light modulator (SLM). According to IDC, a leading provider of technology market intelligence, HDS will begin to replace professional data storage solutions and video devices next year, and by 2010 the organization forecasts that HDS will start replacing consumer video and data optical storage products.
Figure 3: Spatial Light Modulator (SLM)
Holographic data storage breaks through the density limits of conventional storage by recording not only on the surface of the medium, but recording through the medium's full volume. Unlike other optical technologies that record one data bit at a time, holographic storage allows a million bits of data to be written and read in parallel with a single flash of light. This enables transfer rates significantly higher than current optical storage devices.
When used as an SLM, FLCOS delivers a high-speed write rate for data, low overall cost due to its integrated electronics and simplified packaging, and fast volume ramps because of a mature microdisplay manufacturing process. FLCOS technology also offers the high switching speed and optical throughput necessary to effectively switch the deep-blue laser light used in holographic data storage devices. The SLM encodes information onto the data-carrying laser beam that is written into the holographic medium. The SLM maps the electronic data of 0's and 1's into an optical “checkerboard” pattern of more than one million light and dark pixels.
Figure 4: Another view of SLM
FLCOS microdisplays offer a versatile solution to a number of problems facing the consumer electronics engineering community. FLCOS technology has already been proven in the consumer arena, becoming a staple as electronic viewfinders in digital cameras and video camcorders. Now FLCOS microdisplays are being offered in higher resolutions positioning FLCOS to enable a number of different new display applications across many different markets, including the markets described above.
A challenge for all revolutionary technologies is that most consumer electronics are evolutionary. Only when a number of complementary new technologies become available in a relatively short timeframe is a product revolution possible. Today the confluence of FLCOS, high intensity LEDs and lasers and prevalence of consumer video content appears to be enabling a display revolution.
About the author
Bruce F. Spenner has served as Executive Vice President since April 2004 and a director at Displaytech since February 2000. Prior to joining the company, he was employed with Hewlett-Packard Company from 1978 until February 2000, serving in a number of management positions, including Group General Manager and Division General Manager. Prior to joining Hewlett-Packard Company, he both taught and performed research directed towards the application of computers to medicine at Washington University in St. Louis. He serves as a director of the Idaho Research Foundation at the University of Idaho and is a member of the President's Cabinet at California Polytechnic State University and a member of the Idaho Business Council. Dr. Spenner received a D.Sc. degree from Washington University in St. Louis. He can be reached through .