SUNNYVALE, Calif. — Silicon Light Machines, a two-year old startup that uses micro electromechanical systems (MEMS) techniques to form pixels on a silicon chip, has enhanced its Grating Light Valve (GLV) technology to come up with a method that uses only single-dimensional arrays to create an image.

To demonstrate its new approach, Silicon Light Machines engineers built a laser-illuminated HDTV projection display and demonstrated it at the recent Society for Information Display (SID) conference in Anaheim, Calif.

The change from two- to one-dimensional arrays has allowed company engineers to relax certain constraints in the design of their diffraction grating structure. The new devices have higher diffraction efficiency and can perform analog light modulation, not just digital light modulation. The new single-column GLV is a simple micromechanical device consisting of long (100 microns or more), thin (3 microns), flat (100-nanometer) reflective "ribbons" suspended in air by posts at either side. In the original design, a pixel was defined by four shorter ribbons — two fixed ribbons alternating with two movable ones. The movable ribbons are addressed by applying a voltage to the ribbon and an opposite charge to an electrode in the substrate beneath it. The result is a potential difference that "sucks" the ribbon down to the substrate.

When the ribbons are pulled down to one-quarter of the wavelength of the light illuminating the array, the device becomes an efficient diffraction grating and redirects much of the light, creating an "on" pixel. When the active ribbons are not being pulled down, they line up with their neighbors on either side to produce a flat surface. This effectively acts as a mirror, sending all of the light into the reflected beam and away from the image, resulting in an "off" pixel.

The demo HDTV system uses three 1,080-pixel, one-dimensional GLVs to modulate red, green and blue laser light, which is scanned across the display screen at 60 frames per second.

Instead of having an addressable pixel for every image point, each pixel in the new one-dimensional (columnar) GLV array addresses an entire line in every frame as the column scans across. This completely changes the way the device has to operate. For 60 frames/s of binary HDTV (1,920 x 1,080 pixels), this translates to each column pixel switching more than 115,200 times per second.

Instantly, the device became analog, its depth varying with the voltage applied. Each ribbon could now move to produce a quarter-phase shift between itself and its immediate neighbors to make an efficient grating, stay still to be part of a flat reflective surface or take a position anywhere between the two. This had the effect of making the device even faster: It could now produce gray levels in a single switching step. According to the company, the analog response of the GLV is better matched to the eye, producing a smaller change in the low-light region where the eye's response is more sensitive and larger changes in bright regions where light levels are more difficult to differentiate.

Another compelling advantage of the 1-D scanned architecture over a conventional 2-D system is the way it scales. In the 2-D system, doubling the resolution in both dimensions means fabricating four times the number of pixels. This makes a huge difference to the yield as image resolution gets larger. In the two-dimensional case, for instance, an SVGA device with a 90 percent yield will translate to an HDTV device with a 63 percent yield. Even worse, for an SVGA device with a 50 percent yield the corresponding HDTV yield would be just 5 percent.

On the other hand, increasing to HDTV for a one-dimensional device drops the yield to 82 percent and 28 percent, respectively, for the same SVGA yields. On top of that, because the 1-D devices contain considerably fewer pixels, their yields should start out considerably higher. The exact same process that gives a 50 percent yield for an SVGA device should produce a 99.9 percent yield for a single column.

— Sunny Baines is contributing editor to EE Times.

	eeProductCenter Launches SpecSearch®, New Parametric Parts Search Engine In our continuing effort to enhance our site, eeProductCenter introduces SpecSearch® powered by GlobalSpec. Click here.
Free Subscription to EE Times First Name Last Name Company Name Title Email address   Click here for your Free Subscription to EETimes Europe