IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 34, NO. 2, APRIL 2006 385
Study of Various Coplanar Gaps Discharges in ac Plasma Display Panel
Kyung Cheol Choi, Member, IEEE, Nam Hoon Shin, Kyo Sung Lee, Bhum Jae Shin, Member, IEEE, and Seong-Eui Lee
Abstract—To achieve a high luminous efficacy in a plasma dis- play panel, the display characteristics, including the luminance, discharge current, and luminous efficacy, were investigated with various coplanar gaps. The temporal behavior of the infrared emis- sion from 80-, 150-, 200-, and 300- m coplanar gap discharges was also studied. The luminance and luminous efficacy increased as the coplanar gap increased until 200 m. However, when the coplanar gap was 300 m with a fixed barrier rib height of 150 m, the lumi- nous and luminous efficacy suddenly decreased. This phenomenon can be explained by the results of the infrared emission observa- tion, as the discharge shape of the 300- m coplanar gap became narrow when the height of barrier rib was fixed at 150 m. The lu- minous efficacy of the 200- m coplanar gap discharge was about 3.2 lm/W (green cells) when an Ne+4%Xe gas mixture was used as the discharge gas in the alternating current plasma display panel.
Index Terms—Coplanar gap, infrared emission, long gap, lumi- nous efficacy, plasma display panel (PDP).
IT is well known that the glow discharges in an alternating current plasma display panel (ac PDP) with an Ne+Xe gas mixture are very inefficient from the point of view of lumi- nous efficacy, as only 14% of the input energy for discharges is used for emitting ultraviolet (UV) photons . A conven- tional ac PDP utilizes the 147- and 173-nm UV photons emitted from the excited Xe monomer and dimer, respectively, to stim- ulate the photoluminescence phosphor. The 147-nm UV pho- tons are emitted from the excited state of the Xe monomer, while the 173-nm UV photons are emitted from the excited state of the Xe dimer. Thus, the proportion of energy used for electron heating that can be transferred to make more excita- tion particles is important. In fact, the luminous efficacy in an ac PDP is dependent on the UV intensity emitted from the ex- cited species, meaning the electron excitation rate needs to be higher to make more UV photons. Currently, there are two ap- proaches to achieve a high luminous efficacy in an ac PDP. One is to use high Xe content discharges , , and the other is to lengthen the distance between the two sustain electrodes , . Usually, the sustain electrodes in an ac PDP are on the same plate, which is called coplanar. When the concentration of Xe is increased in the Ne+Xe gas-mixture discharge, the electron
Manuscript received April 20, 2005; revised July 24, 2005.
K. C. Choi is with the Department of Electrical Engineering and Computer Science, KAIST, Daejeon 305-701, Korea.
N. H. Shin, K. S. Lee, and B. J. Shin are with the Department of Electronics Engineering, Sejong University, Seoul 147-747, Korea.
S.-E. Lee is with the Department of Advanced Materials Engineering, Korea Polytechnic University, Shiheung City 429-793, Korea.
Digital Object Identifier 10.1109/TPS.2006.872456
heating rate also increases . Yet, the case of long coplanar gap discharges is more complex. Several papers have already re- ported on the application of positive column discharges to an ac PDP , , and demonstrated an improved luminous efficacy.
However, NHK (Japan Broadcasting Corporation) reported that the UV intensity emitted from positive column discharges was lower than that from a negative glow under a high gas pressure . The discharge volume in the display cell of an ac PDP is restricted by the barrier rib. When a positive column is used to obtain a highly efficient discharge mode in an ac PDP, the address electrode is normally utilized to spread the discharge and make a long channel , . In this case, the phosphor layer located on the side of the address electrode interacts more with the micro-plasma, thereby accelerating degradation. Dis- play devices need a higher resolution to realize high-definition images, and PDPs are no exception. Therefore, there is a limi- tation to widening the sustain gap for obtaining positive column discharges.
Accordingly, this paper investigates the display characteris- tics, including the luminance and luminous efficacy, of an ac PDP with various coplanar gaps under the condition of a fixed barrier rib height. When the coplanar gap increases, there should be an optimized distance, as the micro-plasma generated in the pixel is restricted by the phosphor plate. Yet, it is not expected that the luminous efficacy will increase in proportion to the dis- tance of the coplanar gap, as the micro-plasma volume is re- stricted by the phosphor plate and the barrier rib of the ac PDP.
The spatio-temporal behavior of the discharges in an ac PDP with various coplanar gaps is also observed using an intensi- fied charge-coupled device (ICCD) camera in order to determine the relationship between the luminous efficacy and the shape of the coplanar gap discharge, and the optimized distance for the coplanar gap. The pixel geometry depends on the coplanar gap, thus the pixel dimensions need to be considered to de- sign an extended video graphic array (XGA) or high definition (HD) resolution. For example, 0.22 mm 0. 66 mm is needed for an XGA 42-in panel with a stripe-type barrier rib, while 0.16 mm 0.48 mm is needed for an HD 42-in panel, meaning there is not enough room to make long channel discharges to achieve a high luminous efficacy in an ac PDP.
The 4-in plasma display test panels with various coplanar gaps were fabricated based on the schematic drawing in Fig. 1.
Transparent indium–tin–oxide (ITO) was used for the sustain electrodes, i.e., the scan and common electrode, which were formed on the front plate with coplanar gaps of 80, 150, 200,
0093-3813/$20.00 © 2006 IEEE
Fig. 1. Schematic drawing of 4-in test plasma display panel with various coplanar gaps.
Fig. 2. Sustain pulse waveforms applied to scan and common electrode.
300, 500, and 800 m. One test panel consists of different gap.
The width of ITO was 300 m. Next, the bus electrodes were fabricated on the sustain electrodes, then the plate was coated with a 30- m-thick transparent dielectric layer, followed by the deposition of a thin MgO layer 600 nm thick. Meanwhile, the address electrodes were formed on the rear plate, which was then coated with a dielectric layer. The width of address elec- trode was 100 m. Thereafter, stripe shaped barrier ribs with a fixed height of 150 m were fabricated using the sand blast method. Green phosphor coated on the barrier ribs was used to measure the luminance of the various coplanar gap discharges of the test panel. An Ne+4%Xe gas mixture was used as the dis- charge gas and the total gas pressure was 450 torr.
The sustain pulses shown in Fig. 2 were applied to the scan and common electrode in the test panel. The width of the sustain pulse was 4 s, while its frequency and duty ratio was 50 kHz and 20%, respectively. All address electrodes of test panel were grounded.
Fig. 3. Luminance of coplanar gap discharge as function of sustain voltage relative to coplanar gap.
III. RESULTS ANDDISCUSSION
The luminance of the ac test plasma test panel was mea- sured to investigate the influence of the coplanar gap. Fig. 3 shows the luminance of the coplanar gap discharges as a func- tion of the sustain voltage relative to the coplanar gap. The voltage was varied from the minimum sustain voltage to the maximum sustain voltage, where the minimum sustain voltage was defined as the firing-off voltage when one of the multiple on-cells changed to an off-state, while the maximum sustain voltage was defined as the firing-on voltage when one of the multiple off-cells changed to an on-state. The voltage range for the 80- m coplanar gap discharge, also known as the voltage margin, was about 50 V. Since the operation voltage of an ac PDP is usually within the voltage margin, the midpoint value of the voltage margin was used as the operation voltage. As expected, the operation voltage increased as the coplanar gap increased.
Up to the coplanar gap of 200 m, the luminance of the coplanar gap discharge increased as the voltage increased, then the luminance of the 300- m coplanar gap discharge decreased as the voltage increased. However, the luminance of the 500- and 800- m coplanar gap discharges increased again as the voltage increased. When the coplanar gap was 300 m, the luminance suddenly decreased and was dimmer than that of the 200- m coplanar gap discharge, yet the luminance of the 500- and 800- m coplanar gap discharges was not as bright as that of the 300- m coplanar gap discharge. Thus, the 300- m coplanar gap behaved differently from the 80-, 150-, and 200- m coplanar gaps, indicating that the 300- m coplanar gap was a kind of transition region between the 200- and 500- m coplanar gap discharges. For the transition region, the shape of the coplanar gap discharge was different from that of the 200- m coplanar gap discharge, as the discharge area became narrow like a filament, which was observed when the coplanar gap discharge was investigated using an ICCD camera. The decrease of the luminance of 300- m coplanar gap discharge with an increase in sustain voltage was directly due to the decrease of current, as shown in Fig. 4.
CHOI et al.: STUDY OF VARIOUS COPLANAR GAPS DISCHARGES 387
Fig. 4. Discharge current of coplanar gap discharge as function of sustain voltage relative to coplanar gap.
Fig. 4 shows the discharge current of the coplanar gap dis- charge as function of the sustain voltage relative to the coplanar gap. Up to the 200- m coplanar gap, the discharge current in- creased with an increase in the applied sustain voltage. How- ever, the current for the 300- m coplanar gap discharge exhib- ited a different behavior, and when the coplanar gap was more than 300 m, the discharge current gradually decreased as the coplanar gap increased. It is thought that the 300- m coplanar gap discharge is in the subnormal or the normal glow region.
When the coplanar gap was 500 and 800 m, the discharge cur- rent increased again with an increase in sustain voltage. The current and luminance of the 300-, 500-, and 800- m coplanar gap-discharges were less than those of the 200- m coplanar gap discharge. This phenomenon was related to the filament shape of the coplanar long gap discharge in the subpixels of the ac PDP, as when the coplanar gap increased, the electric field between the sustain electrodes was reduced and the discharge current also decreased. The restriction of the discharge volume by the bar- rier rib also was related to the lower current. It is thought that the restriction by the barrier rib was strongly dependent upon the transition region of coplanar gap.
Fig. 5 shows the luminous efficacy of the coplanar gap discharge as a function of the sustain voltage relative to the coplanar gap. Up to the 200- m coplanar gap, the luminous efficacy increased as the coplanar gap increased, then from the 300- m coplanar gap and wider, the luminous efficacy suddenly decreased. As such, the behavior of the luminous efficacy was similar to that of the luminance. The maximum luminous efficacy of the 200- m coplanar gap discharge was about 3.2 lm/W; however, the luminous efficacy of the 300- m coplanar gap discharge was within the range of 1.8–2.1 lm/W.
As mentioned earlier, the discharges of the 300-, 500-, and 800- m coplanar gaps were restricted by the barrier rib and had a narrower channel between the two sustain electrodes. In these cases, even though the discharge current was lower, the luminous efficacy decreased as the luminance was decreased.
Accordingly, when the height of the barrier rib was 150 m, the 200- m coplanar gap for the sustain discharges in the ac PDP was the best value as regards the luminous efficacy.
Fig. 5. Luminous efficacy of coplanar gap discharge as function of sustain voltage relative to coplanar gap.
The infrared (IR) photons with 823- and 828-nm wavelengths were observed using an ICCD camera to investigate the charac- teristics of the various coplanar gap discharges, as 823-nm IR photons are emitted during the transition from the excited state to the metastable state, while 828-nm IR photons are emitted during the transition from the excited state to the excited state. Fig. 6 shows the spatio-temporal behavior of the IR emission from the various coplanar gap discharges.
In the case of the 80- m coplanar gap discharge, the IR emis- sion started in the center between the scan and common elec- trode, then expanded across the scan and common electrode, in- dicating that the 80- m coplanar gap discharge was spreading across the entire subpixel area. Then, when the coplanar gap was 150 m, the IR intensity of the discharge was stronger at the center between the scan and common electrode than with the 80- m coplanar gap discharge. The IR intensity of the 200- m coplanar gap discharge was again much stronger than that of the 150- m coplanar gap discharge, and its volume spread across almost the entire subpixel area. However, when the coplanar gap increased to 300 m, the area of the IR emission was narrowed, as shown in Fig. 6(d), and the distinguishable intensity of the 300- m coplanar gap discharge according to the ICCD camera appeared later than that of the other coplanar gap discharges.
The measuring voltage for the IR emission was the operation voltage. In the center between the scan and common electrode, the area of the IR emission from the 300- m coplanar gap dis- charge became a kind of filament. As already discussed for the results in Figs. 3–5, the main reason for the low luminance of the 300- m coplanar gap discharge was the narrower discharge, as when the coplanar gap in the ac PDP was increased, the volume of the discharge among the subpixels became restricted by the height of the barrier rib. Thus, the IR intensity of the 200- m coplanar gap discharge was found to be the strongest among the 80-, 150-, 200-, and 300- m coplanar gaps, although there still may be a maximum value between the 200- and 300- m coplanar gap. One remaining question, however, is the existence of a critical dimension for the coplanar gap to achieve a high lu- minous efficacy.
Fig. 6. Spatio-temporal behavior of IR emission from various coplanar gap discharges.
The luminance, luminous efficacy, and temporal behavior of various coplanar gap discharges were investigated in an ac PDP.
The luminance of the coplanar gap discharge increased as the coplanar gap increased until 200 m. Then, when the coplanar gap was 300 m, the luminance suddenly decreased and con- tinued to decrease when the sustain voltage was increased.
When the coplanar gaps were 500 and 800 m, the magnitude of the luminance was lower than that for the 200- m coplanar gap. Similar results were obtained for the current and luminous efficacy of the coplanar gap discharges. The maximum lumi- nous efficacy of the 200- m coplanar gap discharge was about
3.2 lm/W, while it was 2.1 lm/W for the 300- m coplanar gap discharge. This phenomenon was explained by observing the IR emission using an ICCD camera. The intensity of the IR emission for the 200- m coplanar gap was the strongest among the other coplanar gap discharges. When the coplanar gap was 300 m, the discharge shape became narrow like a filament.
Thus, a critical dimension was identified for the coplanar gap in an ac PDP as regards obtaining a high luminous efficacy when the height of barrier rib is fixed, and in the present study, a coplanar gap of around 200 m was established as the best condition for a high luminous efficacy in an ac PDP with a barrier rib height of 150 m.
CHOI et al.: STUDY OF VARIOUS COPLANAR GAPS DISCHARGES 389
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Kyung Cheol Choi (M’04) received the B.S. degree from the Department of Electrical Engineering and the M.S. degree and Ph.D. degrees in plasma engi- neering from Seoul National University, Seoul Korea, in 1986, 1988, and 1993, respectively.
He was with the Institute for Advanced Engi- neering, Seoul, Korea, from 1993 to 1995, where his work focused on the design of field emission display devices. He was a Research Scientist in the Microbridge Plasma Display Panel of Spectron Corporation of America, Summit, NJ, from 1995 to 1996. He was a Senior Research Scientist at Hyundai Plasma Display, Hawthorne, NY, from 1996 to 1998, where his work was to continue devel- oping plasma display technology. From 1998 to 1999, he was involved in the development of an ac 40-in plasma display panel at the Advanced Display Research and Development Center of Hyundai Electronics Industries, Gy- ounggi-do, South Korea, as a Senior Research Scientist. From 2000 to 2004, he had been an Associate Professor in the Department of Electronics Engineering, Sejong University, Seoul, Korea. He also was in charge of the Information Display Research Center supported by Korean Ministry of Information and Communication. Since February 1, 2005, he has been an Associate Professor in the Department of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea.
His research interests include plasma display panel, information displays, and micro-plasma applications for laser and bio-electronics.
Dr. Choi is a member of the Society for Information Display and the Korean Information Display Society.
Nam Hoon Shin received the B.S. degree from the Department of Electronics Engineering from Sejong University, Seoul, Korea, in 2004. He is currently working toward the M.S. degree in electronics engineering at the same university. His work focuses on plasma display panel.
Kyo Sung Lee received the B.S. degree from the Department of Information and Communication Engineering from Sejong University, Seoul, Korea, in 2004. He is currently working toward the M.S.
degree in electronics engineering at the same univer- sity. His work focuses on plasma display panel.
Bhum Jae Shin (M’03) graduated from Seoul Na- tional University, Seoul, Korea, in 1990. He received the M.S. and Ph.D. degrees in plasma engineering from Seoul National University, in 1992 and 1997, respectively.
He worked on the development of PDPs as a Senior Researcher in the PDP team of Samsung SDI, Korea, from 1997 to 2000. He worked on the capillary discharges as a Research Scholar in the Physics Department of the Stevens Institute of Technology, Hoboken, NJ, from 2000 to 2001. In 2002, he returned to Korea, and following a one-year postdoctoral at Seoul National University, he is currently working on the development of PDPs as a Assistant Professor in the Electronics Engineering Department of the Sejong University, Seoul, Korea, since 2003.
Seong-Eui Lee received the B.S., M.S., and Ph.D.
degrees, in 1988, 1990, and 1995, respectively, from Seoul National University, Seoul, Korea. During his Ph.D. research, he worked on the phase transforma- tion kinetics of amorphous powder.
After gradation, he joined Hyundai Electronics Korea and worked as a Senior Researcher at the Hyundai Plasma Display Research Center in Japan for the 26-in XGA PDP project. After his PDP work, he joined iFire Technology, Inc., as a Senior Researcher for the Thick Film Technology Devel- opment Group. After returning to Korea, he worked as a Principal Engineer at Samsung Advanced Institute of Technology for thick-film-related display development especially PDP and flexible display. He recently joined Korea Polytechnic University, Shiheung City, as a Faculty Member in the Depart- ment of Advanced Materials Engineering. His main areas of interests are the process development and integration for display based on thick-film or printing technology. He has published more than 20 papers in journal and conference proceedings and holds more than 40 patents.