Randy Hoffner /
05.04.2005 12:00 AM
CRTs Give Way to New Era of Display Technology
Today, it is apparent that the venerable CRT television set that we have been watching since the 1950s is living on borrowed time. This set of circumstances has been brought about by a convergence of factors, including the recent abundance of advanced displays with expanding performance and shrinking price tags; the increasing availability of HDTV programming; and the inconvenience in size and weight of CRT displays, particularly larger ones.

In past columns, we examined some of the new display technologies on their way to replacing the CRT. Some of the advanced display technologies most commonly encountered today include liquid crystal displays (LCDs), plasma display panels (PDPs) and digital micromirror devices (DMDs).

One of the newest display technologies to be seen at the 2005 CES show, and soon to hit the marketplace, is the surface-conduction electron-emission display (SED). Some of the above-mentioned technologies may be applied to flat-panels, some to projectors and some to both.

There are other, less common devices and technologies, but these are the ones we are most likely to encounter. Meanwhile, back in the lab, brand- new technologies are being investigated. Let's look at some of those.

NANOTECHNOLOGY

One new area that is being intensively investigated (not to say mined) is carbon nanotechnologies. Work on carbon nanotechnology for television displays is proceeding in two directions: carbon nanotubes and, yes, diamonds.

The displays using these technologies are called field emission displays, or FEDs, and are thought by their proponents to be capable of delivering better images at less cost and with the expenditure of less energy than LCDs or PDPs.

(click thumbnail)
The Lamina Ceramics ultra-high lumen LED white light engine

In an FED device, an electron emitter is located a short distance from a phosphor screen. This device operates similarly in many respects to a CRT, except that the electron emitter in a CRT--the cathode--must be heated to stimulate electron emission.

In the FED, the emitter device emits electrons using a process called quantum tunneling. Quantum tunneling is a concept that is no less difficult to understand than any other quantum mechanical concept. In essence, it works because under some conditions, an electron is able to jump or "tunnel" through a classically forbidden energy state.

A high voltage propels the emitted electrons across the vacuum gap, causing them to strike a phosphor-coated anode area, which in turn causes the phosphors to glow.

Because the emitters do not require heating, many small emitters may be packed closely, and the distance between emitter and phosphor may be quite short. Thus, the sweeping electron beam of a CRT, and its beam-steering apparatus, are replaced with a separate electron emitter for each pixel. The same phosphors as those used in CRTs may be used, and the net result is said to be a flat-panel display with viewing characteristics that resemble a CRT.

The quantum tunneling process is also said to be much more energy-efficient than a CRT or an ionized plasma display device. A similar quantum tunneling emission and phosphor display mechanism is used in the SED, although the emitter particles used in SEDs are not carbon.

Carbon nanotubes are synthetically generated microtubes comprised of large carbon molecules. The tubes form into cylinders that are about 1 to 3 nanometers in diameter, and hundreds of thousands of nanometers in length. This form of carbon is highly conductive. Companies are now claiming the capability to manufacture substantial quantities of both single- and multiple-walled carbon nanotubes that are suitable for use as FED emitters. Another company is currently trying to develop an FED using another form of carbon--diamond dust.

Bear in mind that not every technology that shows promise in the research lab will become a commercial success. Two recent advanced display technologies offer instructive examples. One of these is organic light emitting devices, or OLEDs, which are organic chemical compounds that emit light when stimulated with electricity.

While OLEDs are found today in small-screen applications such as cell phone and auto radio displays, they have not, as yet, fulfilled their early promise in larger, flat-panel television displays.

Another technology is liquid crystal on semiconductor (LCOS), a device that is a hybrid of DMD and liquid crystal technologies. LCOS was embraced about two years ago, by a number of companies with big, recognizable names, to be used as a microdisplay projection engine. Many, if not most of those companies have dropped their work in the LCOS display area, leaving the continuing development of LCOS to smaller boutique companies. There are many hurdles to clear to turn a promising laboratory breakthrough into a successful commercial product, and time will tell whether these new, cutting edge display technologies find their way into homes or not.

THE LIGHT CONGRESS

In addition to new display engine technologies, the recent Light Congress, held in New York, revealed that other new, interesting technologies with potential television display applications are emerging.

For example, Congress attendees saw a demonstration of a new 28,000-lumen white LED spotlight. To put this into perspective, a 75 W incandescent light bulb generates about 1,000 lumens of light, so this 5-inch-square device containing 1,120 LEDs generates as much light as about 28 75 W bulbs, at a color-corrected temperature of 5,500 Kelvin.

Presumably, this LED spotlight generates much less heat than 28 75 W light bulbs. One of the biggest problems its developers had to overcome, in fact, was to efficiently wick heat away from the LEDs, as heat causes the LED devices to dim and eventually to break down physically.

Another new device shown at the Light Congress was a spectrally programmable light engine. In this device, white light is separated into spectral components by a diffraction grating, and aimed at a digital micromirror device. By properly controlling the micromirrors, both the spectral content of the output light and the intensity of each spectral component appearing in the output, can be controlled. Both of these lighting technologies have interesting implications for flat-panel and projection displays.

These are some of the most recent new developments in display devices and technologies. Others will, without doubt, appear. After a number of decades in which only a single type of display, the CRT, was available, we are now living in an exciting era in television display technology.


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