06-02-2013, 10:54 AM
GRATING LIGHT VALVE DISPLAY TECHNOLOGY
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ABSTRACT
The Cathode Ray Tube TV set has ruled the consumer electronics world for decades. Now a day everyone wants big screens for their entertainment rooms. But bigger a CRT screen, the glass tube will be deeper and the set becomes impossibly heavy and unwieldy when the diagonal measurement of the screen goes beyond about 36 inches. Thus the CRT is destined for a slow but sure decline giving way to many new technologies. The solution comes as grating light valve display technology. The original GLV device concepts were developed at Stanford University. Later Silicon Light Machines was found in 1994 to develop and commercialize a range of products based on this technology. The GLV device is a type of optical micro electromechanical system or MEMS essentially a movable, light reflecting surface created directly on a silicon wafer, utilizing standard semiconductor processes and equipment. A Grating Light Value (GLV) device consists of parallel rows of reflective ribbons. Alternate rows of ribbons can be pulled down approximately one-quarter wavelength to create diffraction effects on incident light (see figure 1). When all the ribbons are in the same plane, incident light is reflected from their surfaces. By blocking light that returns along the same path as the incident light, this state of the ribbons produces a dark spot in a viewing system. When the (alternate) movable ribbons are pulled down, however, diffraction produces light at an angle that is different from that of the incident light. Unblocked, this light produces a bright spot in a viewing system. The Grating Light Valve uses reflection and diffraction to create dark and bright image areas. If an array of such GLV elements is built, and subdivided into separately controllable picture elements, or pixels, then a white-light source can be selectively diffracted to produce an image of monochrome bright and dark pixels. By making the ribbons small enough, pixels can be built with multiple ribbons producing greater image brightness. If the up and down ribbon switching state can be made fast enough, then modulation of the diffraction can produce many gradations of gray and\or colors. There are several means for displaying color images using GLV devices. These include color filters with multiples light valves, field sequential color, and sub-pixel color using "turned" diffraction gratings.
Technology Overview
The technology is based on simple optical principles that everage the wavelike behavior of light by varying interference to control the intensity of light diffracted from each GLV pixel. A GLV array is fabricated using conventional CMOS materials and equipment, adopting techniques from the emerging field of Micro-Electromechanical Systems (MEMS). Pixels are comprised of a series of identical mechanical structures, fabricated using very few masks and processing steps. The end result is a unique combination of high performance, reliability, and low cost at production volumes. A typical GLV pixel is made up of an even number of parallel doubly supported beams, or ribbons.” While pixel dimensions are saleable, a typical design for a 25 mm pixel (as illustrated in Figure 1) might include six ribbons, each about 3 mm wide, and 100 mm long, but only about 100 nm thick. These ribbons are suspended above a thin air gap (typically about 650 nm), allowing them to move vertically relative to the underlying surface. The ribbons are held in tension so that, when not deflected by electrostatic forces, they form a flat surface. To address a pixel, a potential difference is applied between the aluminum layers on alternate
ribbons and the conductive layer in the underlying substrate. This potential difference creates an
electrostatic attraction that deflects every other pixel ribbon downward toward the substrate, and thereby creates a square-well diffraction grating. Precise control of the vertical displacement of the ribbon can be achieved by balancing this electrostatic attraction against the ribbon restoring force; more drive voltage produces more ribbon deflection. Because the electrostatic attraction is inversely proportional to the square of the distance between the conductors, and also because the distances involved are quite small, very strong attractive forces and accelerations can be achieved. These are counter balanced by a very strong tensile restoring force designed into the ribbons. The net result is a robust, highly uniform and repeatable mechanical system. The combination of low ribbon mass, small excursion (about 1/800 of the ribbon length), and large attractive and restoring forces produces extremely fast switching speeds. GLV pixel switching times have been measured down to 20nsec— three orders of magnitude faster than any other spatial light modulator we have seen reported. GLV devices can be operated in either digital or analog modes, enabling great flexibility in system design and product optimization. Digital operation capitalizes on the GLV technology’s tremendous switching speed to achieve shades of gray by alternately switching pixels fully “on” and fully “off” faster than the human eye can perceive. Very accurate gray scale levels are obtained by controlling the proportion of time pixels are on and off. In analog mode, video drivers precisely control the amount of GLV ribbon deflection; pixels are fully “off” when not deflected, and fully “on” when deflected downward exactly one-quarter the wavelength of the incident light. Deflecting GLV ribbons between these two positions creates shades of gray (more precisely, light with the same color as the incident light, but of gray scale intensity). In the Scanned GLV Architecture, a linear array of GLV pixels is used to project a single column of image data. This column is optically scanned at a high rate across a projection screen. The Scanned GLV Architecture gives Silicon Light Machines an enormous advantage in terms of modulator cost. To create a 1,920 x 1,080-pixel HDTV image using Scanned GLV architecture, for example, we need to manufacture, interconnect, and address only a single linear array of 1,080 pixels; other spatial light modulator technologies would have to manufacture (with acceptable yields), interconnect, and address more than 2 million pixels. In addition to cost, there are a large number of other advantages that accrue to the Scanned GLV Architecture when compared to current and emerging technologies.
Advantages and Limitations
Very high production yields due to the small active area per die. Lower costs due to the large number of candidate die that can be manufactured per processed wafer.Scalability to high resolution – linear scaling instead of geometric scaling as resolution increases. Ability to “fine-tune” uniformity after production, due to the relatively small number of active drive channels required. Ability to display different aspect ratios using the same display module (for different car makes or models). Line-sequential color using switched. sources and a single modulator— no color break-up. Smaller optics (lenses and dichroic), as only the smaller dimension of the X by Y image raster must be projected. Optimal coupling to low-cost laser light sources, as the Scanned GLV Architecture makes effective use of line sources, whereas other approaches require more complex, high-quality beam sources. Straightforward integration of drivers and electronics without compromising optical performance, as electronics and mechanics can be “spread out” to the sides of the optically active linear regions. Path to full integration of three linear arrays per chip for the ultimate low-cost, mechanically stable RGB projection device.
Adequate data for reliability does not exist for the GLV. An initial experiment was done that cycled pixels over 300 billion cycles at an accelerated rate (1 MHz for 100 hours), which corresponds to ten years of television use for a color GLV with eight bits of gray scale. The devices were operated with a 25 V square wave in ambient conditions. No pixel damage (in the form of sticking or fusing) was observed. However, recent work suggests that accelerated lifetime testing is not valid, since it doesn’t give the material time to deform plastically or for cracks to grow. A second limitation is that this testing was done on striated devices. It is not known whether the use of surface roughness rather than striations will increase beam cracking or not.
Applications and Future aspects
Inherent GLV attributes make the technology suitable for a wide variety of imaging applications, ranging from convention hall projection systems, to automotive applications, portable communication devices, printers and optical fiber communications. Every successful automotive industry subsystem must meet a unique and stringent set of requirements: it must be low-cost, modular, and reliable over a wide range of temperature, humidity, and vibration/shock. Additionally, automotive display subsystems must be effective in both direct sunlight and near-total darkness. GLV devices inherently meet all of these requirements, making them viable candidates for automotive industry display applications. The Grating Light Valve technology, and the Scanned GLV Architecture which it uniquely enables, together provide a solid, stable, demonstrated methodology for generating real-time, high-resolution color images in a wide variety of applications. The GLV technology’s inherent low cost, modularity, reliability, and wide dynamic range make it a viable candidate for information-intensive and reconfigurable automotive display applications. With the right partnerships to develop successful system designs, GLV technology may become the standard for future automotive industry displays
[attachment=49785]
ABSTRACT
The Cathode Ray Tube TV set has ruled the consumer electronics world for decades. Now a day everyone wants big screens for their entertainment rooms. But bigger a CRT screen, the glass tube will be deeper and the set becomes impossibly heavy and unwieldy when the diagonal measurement of the screen goes beyond about 36 inches. Thus the CRT is destined for a slow but sure decline giving way to many new technologies. The solution comes as grating light valve display technology. The original GLV device concepts were developed at Stanford University. Later Silicon Light Machines was found in 1994 to develop and commercialize a range of products based on this technology. The GLV device is a type of optical micro electromechanical system or MEMS essentially a movable, light reflecting surface created directly on a silicon wafer, utilizing standard semiconductor processes and equipment. A Grating Light Value (GLV) device consists of parallel rows of reflective ribbons. Alternate rows of ribbons can be pulled down approximately one-quarter wavelength to create diffraction effects on incident light (see figure 1). When all the ribbons are in the same plane, incident light is reflected from their surfaces. By blocking light that returns along the same path as the incident light, this state of the ribbons produces a dark spot in a viewing system. When the (alternate) movable ribbons are pulled down, however, diffraction produces light at an angle that is different from that of the incident light. Unblocked, this light produces a bright spot in a viewing system. The Grating Light Valve uses reflection and diffraction to create dark and bright image areas. If an array of such GLV elements is built, and subdivided into separately controllable picture elements, or pixels, then a white-light source can be selectively diffracted to produce an image of monochrome bright and dark pixels. By making the ribbons small enough, pixels can be built with multiple ribbons producing greater image brightness. If the up and down ribbon switching state can be made fast enough, then modulation of the diffraction can produce many gradations of gray and\or colors. There are several means for displaying color images using GLV devices. These include color filters with multiples light valves, field sequential color, and sub-pixel color using "turned" diffraction gratings.
Technology Overview
The technology is based on simple optical principles that everage the wavelike behavior of light by varying interference to control the intensity of light diffracted from each GLV pixel. A GLV array is fabricated using conventional CMOS materials and equipment, adopting techniques from the emerging field of Micro-Electromechanical Systems (MEMS). Pixels are comprised of a series of identical mechanical structures, fabricated using very few masks and processing steps. The end result is a unique combination of high performance, reliability, and low cost at production volumes. A typical GLV pixel is made up of an even number of parallel doubly supported beams, or ribbons.” While pixel dimensions are saleable, a typical design for a 25 mm pixel (as illustrated in Figure 1) might include six ribbons, each about 3 mm wide, and 100 mm long, but only about 100 nm thick. These ribbons are suspended above a thin air gap (typically about 650 nm), allowing them to move vertically relative to the underlying surface. The ribbons are held in tension so that, when not deflected by electrostatic forces, they form a flat surface. To address a pixel, a potential difference is applied between the aluminum layers on alternate
ribbons and the conductive layer in the underlying substrate. This potential difference creates an
electrostatic attraction that deflects every other pixel ribbon downward toward the substrate, and thereby creates a square-well diffraction grating. Precise control of the vertical displacement of the ribbon can be achieved by balancing this electrostatic attraction against the ribbon restoring force; more drive voltage produces more ribbon deflection. Because the electrostatic attraction is inversely proportional to the square of the distance between the conductors, and also because the distances involved are quite small, very strong attractive forces and accelerations can be achieved. These are counter balanced by a very strong tensile restoring force designed into the ribbons. The net result is a robust, highly uniform and repeatable mechanical system. The combination of low ribbon mass, small excursion (about 1/800 of the ribbon length), and large attractive and restoring forces produces extremely fast switching speeds. GLV pixel switching times have been measured down to 20nsec— three orders of magnitude faster than any other spatial light modulator we have seen reported. GLV devices can be operated in either digital or analog modes, enabling great flexibility in system design and product optimization. Digital operation capitalizes on the GLV technology’s tremendous switching speed to achieve shades of gray by alternately switching pixels fully “on” and fully “off” faster than the human eye can perceive. Very accurate gray scale levels are obtained by controlling the proportion of time pixels are on and off. In analog mode, video drivers precisely control the amount of GLV ribbon deflection; pixels are fully “off” when not deflected, and fully “on” when deflected downward exactly one-quarter the wavelength of the incident light. Deflecting GLV ribbons between these two positions creates shades of gray (more precisely, light with the same color as the incident light, but of gray scale intensity). In the Scanned GLV Architecture, a linear array of GLV pixels is used to project a single column of image data. This column is optically scanned at a high rate across a projection screen. The Scanned GLV Architecture gives Silicon Light Machines an enormous advantage in terms of modulator cost. To create a 1,920 x 1,080-pixel HDTV image using Scanned GLV architecture, for example, we need to manufacture, interconnect, and address only a single linear array of 1,080 pixels; other spatial light modulator technologies would have to manufacture (with acceptable yields), interconnect, and address more than 2 million pixels. In addition to cost, there are a large number of other advantages that accrue to the Scanned GLV Architecture when compared to current and emerging technologies.
Advantages and Limitations
Very high production yields due to the small active area per die. Lower costs due to the large number of candidate die that can be manufactured per processed wafer.Scalability to high resolution – linear scaling instead of geometric scaling as resolution increases. Ability to “fine-tune” uniformity after production, due to the relatively small number of active drive channels required. Ability to display different aspect ratios using the same display module (for different car makes or models). Line-sequential color using switched. sources and a single modulator— no color break-up. Smaller optics (lenses and dichroic), as only the smaller dimension of the X by Y image raster must be projected. Optimal coupling to low-cost laser light sources, as the Scanned GLV Architecture makes effective use of line sources, whereas other approaches require more complex, high-quality beam sources. Straightforward integration of drivers and electronics without compromising optical performance, as electronics and mechanics can be “spread out” to the sides of the optically active linear regions. Path to full integration of three linear arrays per chip for the ultimate low-cost, mechanically stable RGB projection device.
Adequate data for reliability does not exist for the GLV. An initial experiment was done that cycled pixels over 300 billion cycles at an accelerated rate (1 MHz for 100 hours), which corresponds to ten years of television use for a color GLV with eight bits of gray scale. The devices were operated with a 25 V square wave in ambient conditions. No pixel damage (in the form of sticking or fusing) was observed. However, recent work suggests that accelerated lifetime testing is not valid, since it doesn’t give the material time to deform plastically or for cracks to grow. A second limitation is that this testing was done on striated devices. It is not known whether the use of surface roughness rather than striations will increase beam cracking or not.
Applications and Future aspects
Inherent GLV attributes make the technology suitable for a wide variety of imaging applications, ranging from convention hall projection systems, to automotive applications, portable communication devices, printers and optical fiber communications. Every successful automotive industry subsystem must meet a unique and stringent set of requirements: it must be low-cost, modular, and reliable over a wide range of temperature, humidity, and vibration/shock. Additionally, automotive display subsystems must be effective in both direct sunlight and near-total darkness. GLV devices inherently meet all of these requirements, making them viable candidates for automotive industry display applications. The Grating Light Valve technology, and the Scanned GLV Architecture which it uniquely enables, together provide a solid, stable, demonstrated methodology for generating real-time, high-resolution color images in a wide variety of applications. The GLV technology’s inherent low cost, modularity, reliability, and wide dynamic range make it a viable candidate for information-intensive and reconfigurable automotive display applications. With the right partnerships to develop successful system designs, GLV technology may become the standard for future automotive industry displays