SCRAM Debuts High-Contrast Screen Technology (Microdisplay Report, Vol 4, No 4) by Chris Chinnock    April, 2001 DisplaySearch’s FPD Conference held in Austin in March was the venue for the official unveiling of a new screen technology. Called the SCRAMscreen, and developed by SCRAM Technologies, Inc., (Dunkirk, MD), it uses a series of tightly packed waveguides to enable thin-profile, high-contrast rear-projection systems. This is a novel and important technology that looks well positioned to have a major impact on the industry. SCRAM Technologies was founded in 1998 to commercialize a rear-screen concept developed at Brookhaven National Labs (Brookhaven, NY). Armed with an exclusive license, the company has been quietly working on perfecting prototypes, expanding its intellectual property, and securing licensing and manufacturing partners. In August 1999, they demonstrated the technology as a 9-inch sunlight-readable display screen in a B-52 aircraft instrumentation module. Since then, many of the pieces of its commercialization plan have come together, and it is ready to begin serious sampling and evaluation projects with customers. For example, eight patents have been issued, 20 more are pending, and 12 are in draft. SCRAM Technologies found a manufacturing partner for the SCRAMscreen, and the company is evaluating partners for associated optical elements like prisms and diffusers. It also signed a licensing deal with Samsung Electronics, Inc. (Suwon City, Korea). Per its business plan, SCRAM Technologies will offer the screen manufacturing technology for free to producers. Users of the screen, such as Samsung, would negotiate with the producers on price, and pay SCRAM a per-screen royalty. Samsung was supposed to debut the screen technology to a European audience at the CeBIT trade exhibition in Germany at the end of March. Key attributes of this technology include high resolution, high contrast and slim form factor when combined with the company’s optical projection system. The SCRAMscreen technology can also be applied to existing rear-screen projection systems to provide similar benefits. While costs of the screen are not yet well determined, preliminary calculations indicate it can be manufactured quite cost competitively. We had a chance to see the new screen technology at the DisplaySearch Conference and it is indeed impressive. On display was a 50-inch prototype projection system that uses the company’s SCRAMscreen technology and custom-developed projection optics. Powering the prototype is a standard 1-chip DLP projector with XGA resolution. The demonstrator was only 9 inches deep and the image quality was quite good. Overall light efficiency of the screen is around 80-84%, and it appears to be faithfully replicating the color saturation, brightness and uniformity of the DLP engine source. Most impressive is the contrast. It actually improved from the 450:1 obtained when measuring the DLP projector in the conventional way, to 600:1 when measured on the SCRAMscreen. This improvement is the result of the construction of the screen, which greatly reduces the effect that ambient light has on reducing the contrast ratio. The SCRAMscreen is constructed in a surprisingly simple manner. To make it, the company starts with thin, clear polymer sheets. To each clear sheet, it laminates a second “Black” polymer sheet with an index of refraction that is lower than the clear sheet. SCRAM Technologies developed some technology to realize a low-index, light-absorbing polymer. “Normally, light-absorbing polymers have a higher index of refraction than the clear polymer,” says company President & CEO, Ray Kwong. This alternating lamination process is continued until a tall stack is obtained. The stack is then cut into a series of thin screens that is a cross-section of the stacked laminations. A polymer-diffusing layer is laminated to the front of the screen to disperse emerging light into a wide field of view. To couple light from a projection source into the screen, the original design cut the lamination stack into a triangular form factor so that the base of the screen was thicker than the top. The company’s custom-designed optical system compresses the image from a light engine in the vertical plane, creating a very thin image. This band of light is projected onto the thicker vase section of the triangularly –shaped screen. This shape channels the light to the different parts of the screen. Key to the SCRAMscreen are the stacked laminations. When light is coupled into each one, the lower-index black layers that sandwich the clear section from an optical waveguide. When light enters the clear polymer channel, it is guided through the screen by total internal reflection. In addition, the black layer enhances the on-screen contrast by absorbing ambient light coming from in front of the screen. This produces better black levels. Each layer in the SCRAMscreen can be made quite thin. In the 50-inch prototype, for example, there are 1500 layers. That means there are three layers for each projected pixel from the XGA engine, resulting in an overscan of the image. SCRAM Technologies says they can even improve on this by nearly doubling the number of layers in a 50-inch screen, thus faithfully reproducing even high-resolution source data. The company has made a series of innovations to this basic design in the last few months. For example, for the 50-inch prototype, the triangular shape has been eliminated in favor of a normal rectangular profile. A specially designed polymer prism is added to the back surface, which collects the light coming in at a sharp oblique angle, and couples it into the waveguides. Another improvement coming soon is a screen with waveguides at a 6-degree angle to the surface normal. This tilt is enough to eliminate a specular reflection that results in the current screen design if an ambient light source is located normal to the screen surface. This location allows ambient light to couple into the waveguide, circumventing the absorbing black layers. On the company’s roadmap is a new 36-inch system that will use a LCOS light engine. This is being developed with Samsung, and will reportedly be only 6 inches deep.