Field emission display
Encyclopedia
A field emission display (FED) is a display technology that incorporates flat panel display
technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor
to produce a color image as a electronic visual display
. In a general sense, a FED consists of a matrix of cathode ray tube
s, each tube producing a single sub-pixel, grouped in threes to form red-green-blue (RGB) pixel
s. FEDs combine the advantages of CRTs, namely their high contrast levels and very fast response times, with the packaging advantages of LCD and other flat panel technologies. They also offer the possibility of requiring less power, about half that of an LCD system.
After considerable time and effort in the early and mid-2000s, Sony's FED efforts started winding down in 2009 as LCD became the dominant technology. In January 2010, AU Optronics
announced that it acquired essential FED assets from Sony and intends to continue development of the technology.
FEDs are closely related to another developing display technology, the surface-conduction electron-emitter display
, or SED, differing primarily in details of the electron emission system. In August 2010, Canon announced they were shutting down their joint effort to develop SEDs commercially, signalling the end of development efforts.
(CRT) with an electron gun
that uses high voltage (10 kV) to accelerate electrons which in turn excite the phosphors, but instead of a single electron gun, a FED display contains a grid of individual nanoscopic electron guns.
A FED screen is constructed by laying down a series of metal stripes onto a glass plate to form a series of cathode lines. Photolithography
is used to lay down a series of rows of switching gates at right angles to the cathode lines, forming an addressable grid. At the intersection of each row and column a small patch of emitters are deposited, typically using methods developed from inkjet printer
s. The metal grid is laid on top of the switching gates to complete the gun structure.
A high voltage-gradient field is created between the emitters and a metal mesh suspended above them, pulling electrons off the tips of the emitters. This is a highly non-linear process and small changes in voltage will quickly cause the number of emitted electrons to saturate. The grid can be individually addressed but only the emitters located at the crossing points of the powered cathode and gate lines will have enough power to produce a visible spot, and any power leaks to surrounding elements will not be visible.
The non-linearity of the process allows avoidance of active matrix addressing schemes – once the pixel lights up, it will naturally glow for some time. Non-linearity also means that the brightness of the sub-pixel is pulse-width modulated
to control the number of electrons being produced, like in plasma displays.
The grid voltage sends the electrons flowing into the open area between the emitters at the back and the screen at the front of the display, where a second accelerating voltage additionally accelerates them towards the screen, giving them enough energy to light the phosphors. Since the electrons from any single emitter are fired toward a single sub-pixel, the scanning electromagnets are not needed.
The efficiency of the field emitters is based on the extremely small radii of the tips, but this small size renders the cathodes susceptible to damage by ion impact. The ions are produced by the high voltages interacting with residual gas molecules inside the device.
FED display requires a vacuum to operate, so the display tube has to be sealed and mechanically robust. However, since the distance between the emitters and phosphors is quite small, generally a few millimeters, the screen can be mechanically reinforced by placing spacer strips or posts between the front and back face of the tube.
FEDs require high vacuum levels which are difficult to attain: the vacuum suitable for conventional CRTs and vacuum tubes is not sufficient for long term FED operation. Intense electron bombardment of the phosphor layer will also release gas during use.
and the electromagnets used to steer the beam, and are thus much more power efficient than a CRT of similar size.
fluorescent lamp
s or high-power white LED
s, the overall efficiency of an LCD display is not very high. Although the lighting process used in the FED is less efficient, only lit sub-pixels require power, which means that FEDs are more efficient than LCDs. Sony
's 36" FED prototypes have been shown drawing only 14 W when displaying brightly lit scenes, whereas a conventional LCD screen of similar size would normally draw well over 100 W.
Avoiding the need for a backlighting system and thin-film transistor
active matrix also greatly reduces the complexity of the set as a whole, while also reducing its front-to-back thickness. While a FED has two sheets of glass instead of the one in an LCD, the overall weight is likely to be less than a similarly sized LCD. FEDs are also claimed to be cheaper to manufacture, as they have fewer total components and processes involved. However, they are not easy devices to manufacture as a reliable commercial device, and considerable production difficulties have been encountered. This had led to a race with two other front-running technologies aiming to replace LCDs in television use, the Active-Matrix OLED
and surface-conduction electron-emitter display
, or SED.
s (OLED) are similar to the LCDs but replace the backlights and polarizing cells with an OLED cell that directly emits light. They require no separate light source, and are highly efficient in terms of light output. They offer the same high contrast levels and fast response times that FED offers. OLEDs are a serious competitor to FEDs, but suffer from the same sorts of problems bringing them to mass production.
. SED has been considered to be the variant of FED that is feasible to mass-produce, however, as of late 2009 no commercial SED display products have been made available by the industry.
cones known as Spindt tips. They suffered from erosion due to the high accelerating voltages. Attempts to lower accelerating voltages and find suitable phosphors that would work at lower power levels, as well as address the erosion problem through better materials, were unsuccessful.
Candescent pushed ahead with development in spite of problems, breaking ground on a new production facility in Silicon Valley
in 1998, partnering with Sony
. However the technology was not ready, and the company suspended equipment purchases in early 1999, citing "contamination issues".
The plant was never completed, and after spending $600 million on development they filed for Chapter 11 protection in June 2004, and sold all of their assets to Canon that August.
Another attempt to address the erosion issues was made by Advance Nanotech, a subsidiary of SI Diamond Technology of Austin, Texas
. Advance Nanotech developed a doped diamond dust, whose sharp corners appeared to be an ideal emitter. However the development never panned out and was adandoned in 2003. Advance Nanotech then applied their efforts to the similar SED display, licensing their technology to Canon. When Canon brought in Toshiba
to help developing the display, Advance Nanotech sued, but ultimately lost in their efforts to re-negotiate the contracts based on their claim that Canon transferred the technology to Toshiba.
Recent FED research focuses on carbon nanotube
s (CNTs) as emitters. Nano-emissive display (NED) is Motorola's term for their carbon-nanotube-based FED technology. A prototype model was demonstrated in May 2005, but Motorola has now halted all FED-related development.
Futaba Corporation has been running a Spindt-type development program since 1990. They have produced prototypes of smaller FED systems for a number of years and demonstrated them at various trade shows, but like the Candescent efforts no large-screen production has been forthcoming. Development continues on a nanotube based version.
Sony, having abandoned their efforts with Candescent, licensed CNT technology from Carbon Nanotechnologies Inc.
,
of Houston, Texas
, who were the public licensing agent for a number of technologies developed at Rice University
's Carbon Nanotechnology Laboratory. In 2007 they demonstrated a FED display at a trade show in Japan and claimed they would be introducing production models in 2009. They later spun off their FED efforts to "Field Emission Technologies", which continued to aim for a 2009 release.
Their plans to start production at a former Pioneer factory in Kagoshima were delayed by financial issues in late 2008. On March 26, 2009 "Field Emission Technologies" (FET) announced that it was closing down due to the inability to raise capital.
In January 2010, Taiwanese AU Optronics
Corporation (AUO) announced that it had acquired assets from Sony's FET and FET Japan, including "patents, know-how, inventions, and relevant equipment related to FED technology and materials". In November 2010, Nikkei
reported that AUO plans to start mass production of FED panels in the fourth quarter of 2011, however AUO commented that the technology is still in the research stage and there are no plans to begin mass production at this moment.
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
to produce a color image as a electronic visual display
Electronic visual display
An electronic visual display is display technology which incorporates flat panel displays, performs as a video display, output device for presentation of images transmitted electronically, for visual reception, without producing a permanent record....
. In a general sense, a FED consists of a matrix of cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s, each tube producing a single sub-pixel, grouped in threes to form red-green-blue (RGB) pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s. FEDs combine the advantages of CRTs, namely their high contrast levels and very fast response times, with the packaging advantages of LCD and other flat panel technologies. They also offer the possibility of requiring less power, about half that of an LCD system.
After considerable time and effort in the early and mid-2000s, Sony's FED efforts started winding down in 2009 as LCD became the dominant technology. In January 2010, AU Optronics
AU Optronics
AU Optronics was formed in December 2001 by the merger of Acer Display Technology, Inc., and Unipac Optoelectronics Corporation. In October 2006, AUO merged with Quanta Display Inc. to create a leading TFT-LCD manufacturer. Additionally, the amassed production of the company's G6 reached worldwide...
announced that it acquired essential FED assets from Sony and intends to continue development of the technology.
FEDs are closely related to another developing display technology, the surface-conduction electron-emitter display
Surface-conduction Electron-emitter Display
A surface-conduction electron-emitter display is a display technology which is currently developing various flat panel displays by a number of companies as a electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image...
, or SED, differing primarily in details of the electron emission system. In August 2010, Canon announced they were shutting down their joint effort to develop SEDs commercially, signalling the end of development efforts.
Operation
FED display operates like a conventional cathode ray tubeCathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRT) with an electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
that uses high voltage (10 kV) to accelerate electrons which in turn excite the phosphors, but instead of a single electron gun, a FED display contains a grid of individual nanoscopic electron guns.
A FED screen is constructed by laying down a series of metal stripes onto a glass plate to form a series of cathode lines. Photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
is used to lay down a series of rows of switching gates at right angles to the cathode lines, forming an addressable grid. At the intersection of each row and column a small patch of emitters are deposited, typically using methods developed from inkjet printer
Inkjet printer
An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...
s. The metal grid is laid on top of the switching gates to complete the gun structure.
A high voltage-gradient field is created between the emitters and a metal mesh suspended above them, pulling electrons off the tips of the emitters. This is a highly non-linear process and small changes in voltage will quickly cause the number of emitted electrons to saturate. The grid can be individually addressed but only the emitters located at the crossing points of the powered cathode and gate lines will have enough power to produce a visible spot, and any power leaks to surrounding elements will not be visible.
The non-linearity of the process allows avoidance of active matrix addressing schemes – once the pixel lights up, it will naturally glow for some time. Non-linearity also means that the brightness of the sub-pixel is pulse-width modulated
Pulse-width modulation
Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
to control the number of electrons being produced, like in plasma displays.
The grid voltage sends the electrons flowing into the open area between the emitters at the back and the screen at the front of the display, where a second accelerating voltage additionally accelerates them towards the screen, giving them enough energy to light the phosphors. Since the electrons from any single emitter are fired toward a single sub-pixel, the scanning electromagnets are not needed.
Disadvantages
Just like any other displays with individually addressable sub-pixels, FED displays can potentially suffer from manufacturing problems that will result in dead pixels. However, the emitters are so small that many "guns" can power a sub-pixel, the screen can be examined for dead emitters and brightness corrected by increasing the pulse width to make up for the loss through increased emissions from the other emitters feeding the same pixelThe efficiency of the field emitters is based on the extremely small radii of the tips, but this small size renders the cathodes susceptible to damage by ion impact. The ions are produced by the high voltages interacting with residual gas molecules inside the device.
FED display requires a vacuum to operate, so the display tube has to be sealed and mechanically robust. However, since the distance between the emitters and phosphors is quite small, generally a few millimeters, the screen can be mechanically reinforced by placing spacer strips or posts between the front and back face of the tube.
FEDs require high vacuum levels which are difficult to attain: the vacuum suitable for conventional CRTs and vacuum tubes is not sufficient for long term FED operation. Intense electron bombardment of the phosphor layer will also release gas during use.
CRT
FEDs eliminate much of the electrical complexity of a CRT, including the heated filaments in the electron gunElectron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
and the electromagnets used to steer the beam, and are thus much more power efficient than a CRT of similar size.
LCD
Flat-panel LCD displays use a bright light source and filter out half of the light with a polarizer, and then filter most of the light to produce red green and blue (RGB) sources for the sub-pixels. That means that only 1/6 (or less in practice) of the light being generated at the back of the tube reaches the screen, at best. In most cases the LCD itself then filters out additional light in order to change the brightness of the sub-pixels and produce a color gamut. So in spite of using extremely efficient light sources like cold cathodeCold cathode
A cold cathode is a cathode used within nixie tubes, gas discharge lamps, discharge tubes, and some types of vacuum tube which is not electrically heated by the circuit to which it is connected...
fluorescent lamp
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...
s or high-power white LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s, the overall efficiency of an LCD display is not very high. Although the lighting process used in the FED is less efficient, only lit sub-pixels require power, which means that FEDs are more efficient than LCDs. Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
's 36" FED prototypes have been shown drawing only 14 W when displaying brightly lit scenes, whereas a conventional LCD screen of similar size would normally draw well over 100 W.
Avoiding the need for a backlighting system and thin-film transistor
Thin-film transistor
A thin-film transistor is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid...
active matrix also greatly reduces the complexity of the set as a whole, while also reducing its front-to-back thickness. While a FED has two sheets of glass instead of the one in an LCD, the overall weight is likely to be less than a similarly sized LCD. FEDs are also claimed to be cheaper to manufacture, as they have fewer total components and processes involved. However, they are not easy devices to manufacture as a reliable commercial device, and considerable production difficulties have been encountered. This had led to a race with two other front-running technologies aiming to replace LCDs in television use, the Active-Matrix OLED
Active-Matrix OLED
AMOLED is a display technology for use in mobile devices and televisions. OLED describes a specific type of thin-film display technology in which organic compounds form the electroluminescent material, and active matrix refers to the technology behind the addressing of pixels.As of 2011, AMOLED...
and surface-conduction electron-emitter display
Surface-conduction Electron-emitter Display
A surface-conduction electron-emitter display is a display technology which is currently developing various flat panel displays by a number of companies as a electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image...
, or SED.
OLED
Organic light-emitting diodeOrganic light-emitting diode
An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s (OLED) are similar to the LCDs but replace the backlights and polarizing cells with an OLED cell that directly emits light. They require no separate light source, and are highly efficient in terms of light output. They offer the same high contrast levels and fast response times that FED offers. OLEDs are a serious competitor to FEDs, but suffer from the same sorts of problems bringing them to mass production.
SED
SEDs are very similar to FEDs, the primary difference between the two technologies is that SED uses a single emitter for each column instead of the individual spots of the FED. Whereas a FED uses electrons emitted directly toward the front of the screen, the SED uses electrons that are emitted from the vicinity of a small "gap" in a surface-conducting track laid down parallel to the plane of the panel, and extracted sideways to their original direction of motion. SED uses an emitter array based on palladium oxide laid down by an inkjet or silk-screen processScreen-printing
Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate...
. SED has been considered to be the variant of FED that is feasible to mass-produce, however, as of late 2009 no commercial SED display products have been made available by the industry.
History
The first concentrated effort to develop FED systems started in 1991 by Silicon Video Corporation1, later Candescent Technologies. Their "ThinCRT" displays used metal emitters, originally built out of tiny molybdenumMolybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
cones known as Spindt tips. They suffered from erosion due to the high accelerating voltages. Attempts to lower accelerating voltages and find suitable phosphors that would work at lower power levels, as well as address the erosion problem through better materials, were unsuccessful.
Candescent pushed ahead with development in spite of problems, breaking ground on a new production facility in Silicon Valley
Silicon Valley
Silicon Valley is a term which refers to the southern part of the San Francisco Bay Area in Northern California in the United States. The region is home to many of the world's largest technology corporations...
in 1998, partnering with Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
. However the technology was not ready, and the company suspended equipment purchases in early 1999, citing "contamination issues".
The plant was never completed, and after spending $600 million on development they filed for Chapter 11 protection in June 2004, and sold all of their assets to Canon that August.
Another attempt to address the erosion issues was made by Advance Nanotech, a subsidiary of SI Diamond Technology of Austin, Texas
Austin, Texas
Austin is the capital city of the U.S. state of :Texas and the seat of Travis County. Located in Central Texas on the eastern edge of the American Southwest, it is the fourth-largest city in Texas and the 14th most populous city in the United States. It was the third-fastest-growing large city in...
. Advance Nanotech developed a doped diamond dust, whose sharp corners appeared to be an ideal emitter. However the development never panned out and was adandoned in 2003. Advance Nanotech then applied their efforts to the similar SED display, licensing their technology to Canon. When Canon brought in Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
to help developing the display, Advance Nanotech sued, but ultimately lost in their efforts to re-negotiate the contracts based on their claim that Canon transferred the technology to Toshiba.
Recent FED research focuses on carbon nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
s (CNTs) as emitters. Nano-emissive display (NED) is Motorola's term for their carbon-nanotube-based FED technology. A prototype model was demonstrated in May 2005, but Motorola has now halted all FED-related development.
Futaba Corporation has been running a Spindt-type development program since 1990. They have produced prototypes of smaller FED systems for a number of years and demonstrated them at various trade shows, but like the Candescent efforts no large-screen production has been forthcoming. Development continues on a nanotube based version.
Sony, having abandoned their efforts with Candescent, licensed CNT technology from Carbon Nanotechnologies Inc.
,
of Houston, Texas
Houston, Texas
Houston is the fourth-largest city in the United States, and the largest city in the state of Texas. According to the 2010 U.S. Census, the city had a population of 2.1 million people within an area of . Houston is the seat of Harris County and the economic center of , which is the ...
, who were the public licensing agent for a number of technologies developed at Rice University
Rice University
William Marsh Rice University, commonly referred to as Rice University or Rice, is a private research university located on a heavily wooded campus in Houston, Texas, United States...
's Carbon Nanotechnology Laboratory. In 2007 they demonstrated a FED display at a trade show in Japan and claimed they would be introducing production models in 2009. They later spun off their FED efforts to "Field Emission Technologies", which continued to aim for a 2009 release.
Their plans to start production at a former Pioneer factory in Kagoshima were delayed by financial issues in late 2008. On March 26, 2009 "Field Emission Technologies" (FET) announced that it was closing down due to the inability to raise capital.
In January 2010, Taiwanese AU Optronics
AU Optronics
AU Optronics was formed in December 2001 by the merger of Acer Display Technology, Inc., and Unipac Optoelectronics Corporation. In October 2006, AUO merged with Quanta Display Inc. to create a leading TFT-LCD manufacturer. Additionally, the amassed production of the company's G6 reached worldwide...
Corporation (AUO) announced that it had acquired assets from Sony's FET and FET Japan, including "patents, know-how, inventions, and relevant equipment related to FED technology and materials". In November 2010, Nikkei
Nihon Keizai Shimbun
is one of the largest media corporations in Japan. Nikkei specializes in publishing financial, business and industry news. Its main news publications include:* Nihon Keizai Shimbun , a leading economic newspaper....
reported that AUO plans to start mass production of FED panels in the fourth quarter of 2011, however AUO commented that the technology is still in the research stage and there are no plans to begin mass production at this moment.
See also
- Comparison of display technologyComparison of display technologyThis is a comparison of various properties of different display technologies.- General characteristics :- Temporal characteristics :Different display technologies have vastly different temporal characteristics, leading to claimed perceptual differences for motion, flicker, etc.The figure shows a...
- Field emitter arrayField emitter arrayA field emitter array is a particular form of large-area field electron source. FEAs are prepared on a silicon substrate by lithographic techniques similar to those used in the fabrication of integrated circuits. Their structure consists of a very large number of individual, similar, small field...
- Field electron emission
- Surface-conduction electron-emitter displaySurface-conduction Electron-emitter DisplayA surface-conduction electron-emitter display is a display technology which is currently developing various flat panel displays by a number of companies as a electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image...
(SED)
External links
- AU Optronics - FED display technology]
- FED TV Reviews and News
- Carbon TVs to edge out liquid crystal, plasma?, article from CNETCNETCNET is a tech media website that publishes news articles, blogs, and podcasts on technology and consumer electronics. Originally founded in 1994 by Halsey Minor and Shelby Bonnie, it was the flagship brand of CNET Networks and became a brand of CBS Interactive through CNET Networks' acquisition...
News.com - Nanotechweb article on Motorola prototype
- Candescent and Sony to Jointly Develop FED Technology
- Field Emission Technologies