Field emission display

A field-emission display (FED) is a flat panel display technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor to produce a color image. In a general sense, an FED consists of a matrix of cathode ray tubes, each tube producing a single sub-pixel, grouped in threes to form red-green-blue (RGB) pixels. 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. A field-emission display (FED) is a flat panel display technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor to produce a color image. In a general sense, an FED consists of a matrix of cathode ray tubes, each tube producing a single sub-pixel, grouped in threes to form red-green-blue (RGB) pixels. 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. Sony was the major proponent of the FED design and put considerable research and development effort into the system during the 2000s. Sony's FED efforts started winding down in 2009, as LCD became the dominant flat-panel technology. In January 2010, AU Optronics announced that it acquired essential FED assets from Sony and intends to continue development of the technology. As of 2016, no large-scale commercial FED production has been undertaken. FEDs are closely related to another developing display technology, the surface-conduction electron-emitter display (SED), differing primarily in details of the electron-emission system. FED display operates like a conventional cathode ray tube (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, an FED display contains a grid of individual nanoscopic electron guns. An 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 is deposited, typically using methods developed from inkjet printers. 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 from 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, 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. 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. 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 pixel brightness corrected by increasing the pulse width to make up for the loss through increased emissions from the other emitters feeding the same pixel. FEDs eliminate much of the electrical complexity of cathode ray tubes, including the heated filaments in the electron gun used to generate electrons and the electromagnets in the deflection yokes used to steer the beam, and are thus much more power efficient than a CRT of similar size. However, FEDs are technically worse than CRTs, as they are not capable of multiscanning.