Selasa, 30 Oktober 2007

Mengenal teknologi plasma

Theme: Efficiency of Plasma Display Panels (PDPs)

by Iwan

Recently, plasma display panel (PDP) is able to provide high quality image and performance, also can compete with cathode ray tube (CRT) technology, liquid crystal display (LCD), light emitting diode (LED), etc. The success PDP will depend on the cost fabrication and improvement technology must come out in research. Even improvement technology is doing in time, PDP has main issues such as efficiency, life time, and false colors which are should carry out in the future.
This paper reviewed some basics understanding of plasma, plasma display panel (PDP) and improvement of efficiency of plasma display panel as part of those issues.

The word “plasma" was presented in 1929 by Dr. Irving Langmuir (an American chemist and physicist, 1932 Nobel laureate in Chemistry), which means “moldable substance” or jelly . Plasma is an ionized gas or a set of quasi neutral particle with free electric charge carriers with collective behavior. In an ordinary gas each atom contains an equal number of positive and negative charges. The positive charges in the nucleus are surrounded by an equal number of negatively charged electrons, and each atom is electrically neutral. Gas becomes plasma when the addition of heat or other energy causes a significant number of atoms to release some or all of their electrons. The remaining parts of those atoms are left with a positive charge, and the separated negative electrons are free to move. Those atoms and the resulting electrically charged gas are said to be ionized. When enough atoms are ionized to significantly affect the electrical characteristics of the gas, it is called plasma. Intrinsically it has many interactions between charge particles and neutral particles. Those interactions can determine usefulness and behavior of plasma. Plasma can be generated by energy to release band electrons from atom to make plasma. The energy can be of various origins, such as thermal, electric or light.

Plasma display panel
Plasma display panel (PDP) was invented in the 1964 by researcher at the University of Illinois with first has a single color display. Plasma display panels (PDP) is one of the leading candidates in the competition for large size, high-brightness flat panel displays, suitable for high-definition television monitors. The advantages of PDP are high resolution, fast response, wide viewing angle, low weight, and simple manufacturing process for fabrication . The fact it was expected to be the next generation of TV displays is noticeable in the remarkable recent progress of PDP technology development and manufacturing2.
PDP is using plasma which consider as cold plasma. It means that the background gas stays relatively cold while the electrons or ions in the plasma are heated by the applied voltage. When the hot electrons collide with the background gas atoms and transfer energy to them, many of those atoms respond by emitting UV radiation. The operating conditions of the display (gas composition, pressure, voltage, geometry, etc.) can provide potential performance requirements, such as low voltage operation, long life, high brightness and high contrast.
The plasma display itself is a simple device consisting of two parallel glass plates separated by a precise spacing of some tenths of a millimeter and sealed around the edges. The schematic of PDP can seen in figure 1.

Fig 1. Schematic of plasma display panel
The space between the plates is filled with a mixture of rare gases at a pressure somewhat less than one atmosphere. Parallel stripes of transparent conducting material with a width of about a tenth of a millimeter are deposited on each plate, with the stripes on one plate perpendicular to those on the other. These stripes are the electrodes to which voltages are applied. The intersections of the rows of electrodes on one side and the columns of electrodes on the opposite glass plate define the individual color elements or cells of a PDP. For high quality color images it is important to keep the UV radiation from passing between cells.
Nowadays, plasma display panel (PDP) has some characteristics such as large screens, excellent image quality and brightness, viewing angle is greater than 160°, perfectly flat and perform well even in bright environments. Even though, the main issues of PDP industries are efficiency, lifetime, false contour and those are still investigated to get high quality of PDP.

Improvement of efficiency of plasma display panel
J.P Boeuf2 reported one of the reasons for the low efficacy of PDP discharge is that a large part of the energy is wasted in ion heating (more than 60%). Also the part of the electron energy that is used for xenon excitation is relatively low (less than 50%). Another decrease in efficiency comes about in the processes leading to the conversion of emitted vacuum ultra violet (VUV) photons to useful visible photons reaching the user. Sato et all reported T shaped electrode structure combine by waffle rib structure enhanced up to 40% luminous efficiency.

Fig 2. Schematic of T structure-waffle rib2

G. Veronis et all3 reported Efficiency is an increasing function of Xe concentration in Ne–Xe and He–Xe mixtures and the addition of Ar to Ne–Xe mixtures does not lead to any significant improvement in PDP performance, either in terms of luminous efficiency or breakdown voltage level. G. Veronis et all also explained the efficiency of PDP can be improved  40% by combining waveform and cell geometry design.
Weber proposed positive column (with coplanar gap 500 mikron) alternating current (AC) PDP, the oprating voltage is larger, between 250V-300V. The concept of positive column AC PDP looks promising and variations around this concept may lead to a design combining long discharge path and low operating voltage. This could be achieved by using auxiliary electrodes that would help trigger the discharge at low voltage and quickly lead to the formation of a long path discharge2.

One of the main issues in PDP industries is the efficiency. The efficiency improvement can be realized by cell design, gas mixture, and operating condition. Instead of these, to reduce low cost the PDP production, the fabrication and technology improvement that must come out of research lab in time.

J.P. Boeuf, j. appl. Phys 36, R53-R79,2003
G. Veronis et all, IEEE Transactions on Plasma Science 28, 2000
Sato et all, j. SID 10, 17, 2000
G. Veronis et all, IEEE Transactions on Plasma Science 33, 2005
Weber L F 2001 US Patent 6184848B1

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