High-Resolution Plasma Display Panel (PDP)
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UDC 621.397.132 High-resolution Plasma Display Panel (PDP) VKeiichi Betsui VFumihiro Namiki VYoshikazu Kanazawa VHiroshi Inoue (Manuscript received September 24, 1999) We have developed two types of high-resolution plasma display panels (PDPs): a 25-inch SXGA (1280 × 1024) panel for engineering workstations (EWSs) and personal computers (PCs), and a 42-inch 1024 × 1024 panel for HDTV. First, this paper investi- gates the discharge characteristics of small PDP cells. Then, this paper describes some of the features of the new panels, for example, the improved characteristics of their cells and their unique Alternate Lighting of Surfaces (ALIS) discharge method, which improves both the resolution and the brightness of the panels. 1. Introduction developed a new panel fabrication process and Plasma display panels (PDPs) can be made studied panel characteristics (e.g., driving voltage in large sizes and are expected to be the best can- margin, luminance, and luminance efficiency) and didates for wall-mount displays that are too big high-speed driving methods. In the Japan Elec- to be made using CRTs (i.e., 40-inch and larger). tronics Show held in 1997, we exhibited a PDPs have so far been used mainly for TVs with prototype 25-inch-diagonal SXGA color PDP. the relatively small number of pixels used in the Also, we developed a new high-resolution display VGA format (640 × 480 pixels). This is because panel for TVs using the Alternate Lighting of the discharge control of small pixels has been dif- Surfaces (ALIS) driving method, which is com- ficult. However, broadcasting of high-definition pletely different from conventional ones. As a TV (HDTV) will start when digital TV broadcast- result of our efforts, we succeeded in commercial- ing begins, and resolutions exceeding one million izing a practical PDP that has enough luminance, pixels will be required even for standard TV units. luminance efficiency, and resolution for TVs. Also, the monitors for personal computers (PCs) This paper mainly describes the discharge and workstations (WSs) are being equipped with cell size, discharge characteristics, and driving bigger and higher resolution screens and the method of the 25-inch SXGA PDP and 42-inch demand for 20-inch and larger high-resolution ALIS HDTV panel we have released on the CRT monitors is increasing. Because of their market. space-saving advantage over CRTs and other considerations, the arrival of a large flat-panel 2. High-resolution PDP for workstations display is eagerly awaited in the 60-million-unit The major reason for the high demand for market for large monitors. flat panel displays for PCs and WSs is that they To meet these demands for a high-resolution need a smaller installation space than CRT mon- display, we decided to develop a high-resolution itors. An ordinary 17-inch CRT monitor is at least PDP with surface discharge type cells. We also 40 cm deep and occupies more than half of the FUJITSU Sci. Tech. J.,35,2,pp.229-239(December 1999) 229 K. Betsui et al.: High-resolution Plasma Display Panel (PDP) depth of a standard office desk. This large depth 2) Panel characteristics of CRT monitors makes the distance between the A cell structure technology for a practical operator and the screen (hereinafter called the “op- driving voltage margin, luminance, and luminance eration distance”) as short as 40 to 50 cm. At this efficiency. distance, the proper size of a screen should be 14 3) High-speed driving method to 17 inches in consideration of the angle of the A drive technology for addressing a large movement of the operator’s eyes. What then would number of scan lines (twice as many as on a VGA be the optimal screen size of a thin, flat panel dis- panel) without using the expensive dual scan drive play when it is installed on an office desk? If a method. flat panel display is installed at the back of the desk so that the amount of free desk space is max- 2.1 Basic study of high-resolution PDP imized, the operation distance will be 70 to 80 cm. 2.1.1 Panel structure and Then, to obtain the same optimal angle of eye fabrication process movement, the diagonal screen size of the flat For our high-resolution PDP, we avoided us- panel display should be 21 to 25 inches. Regard- ing a complex panel structure and basically ing the resolution, we decided to design a adopted a three-electrode surface discharge type high-resolution PDP with at least 1280 × 1024 structure which had already been used for large pixels (SXGA) so the operator can read 10.5-point PDPs and has a low manufacturing cost. Figure 1 characters easily and use the PDP for computer- shows the cell structure of our prototype high- aided design (CAD). resolution PDP. Compared to conventional large PDPs for In this paper, a unit discharge area corre- TVs, the high-resolution PDP we developed is sponding to a color is called a “discharge cell,” a smaller and has a higher resolution (at least twice unit area consisting of the three primary colors is as many scan lines as a conventional large PDP). called a “pixel,” and the cell pitch in the horizon- To attain this, we developed the following three tal (line) direction is called the “rib pitch.” technologies. The key fabrication technologies for the high- 1) Panel fabrication processes resolution PDP enable the fabrication of Processing technologies for fabricating fine- fine-pitched barrier ribs (having a pitch nearly half pitched narrow barrier ribs of the required height that of conventional PDPs) and the formation of and for forming phosphor layers uniformly be- uniform phosphor layers between the barrier tween the barrier ribs for sufficient discharge ribs.1) We improved the conventional sand blast- space. ing method and developed a new technology for fabricating ribs that are 30 µm wide and 100 µm Front glass substrate high and have a rib pitch of 110 µm. We also de- Barrier rib veloped a new technology for forming highly Dielectric layer accurate phosphor layers using a photosensitive & MgO phosphor paste. These technologies enabled us to make an experimental panel to test pixels of an R G arbitrary size at pixel pitches of 0.33 mm or more. B Phosphors Display electrodes Figure 2 shows SEM images of the barrier ribs Rear glass substrate we fabricated for the 42-inch PDP and the ones Address electrodes we fabricated for the high-resolution PDP. The Figure 1 barrier ribs have almost the same heights, but the Structure of experimental panel. pitch of the barrier ribs for the high-resolution 230 FUJITSU Sci. Tech. J.,35, 2,(December 1999) K. Betsui et al.: High-resolution Plasma Display Panel (PDP) PDP is about one-third of the pitch of the barrier in each discharge cell. In general, an ion sheath ribs for the 42-inch TVs. of around 30 µm thick is formed on the inner wall 2.1.2 Physical limitations of of each discharge cell of the PDP. discharge cell size Based on the assumption that the narrowest It has been reported that the minimum dis- barrier rib that can be fabricated is 20 µm, the charge cell size required to provide a sufficiently cell pitch must be at least 80 µm when an ion high luminance and a high luminance efficiency sheath of 30 µm thick is formed on both sides of is around 30 mm, which corresponds to the diam- each barrier rib. In consideration of the thick- eter of a common fluorescent tube. If the discharge ness of the phosphor formed on the side walls of space is less than 30 mm, the discharge voltage each rib and the practical maximum limit of the will increase and the luminance efficiency will discharge voltage, the practical limits of cell pitch decrease. With a surface-discharge type cell struc- and pixel pitch should be around 100 µm and ture having straight ribs, there is less discharge 300 µm, respectively. space that can be effectively used. This is because 2.1.3 Discharge cell size and not only is the rib pitch one-third of the pixel pitch discharge voltage in the row direction but also the rib pitch is af- As described above, we had to consider the fected by the rib width, the thickness of the thickness of the ion sheath when deciding the pixel phosphor on the side walls, and the thickness of pitch for the high-resolution PDP. We therefore the ion sheath formed around each rib. investigated the relation between the rib pitch and We could easily see that the discharge char- discharge characteristics. acteristics of the high-resolution PDP would We made a 12-inch-diagonal test panel with largely depend on the cell size in the line direc- rib pitches from 0.11 to 0.56 mm (pixel pitch: 0.33 tion. The ion sheath is a dark space that forms to 1.68 mm) and measured the static discharge- between a conductor or insulator and a plasma. voltage characteristics of a small area (about The inside of the ion sheath is not electrically neu- 20 mm × 30 mm). Figure 3 shows the changes in tral. The ion sheath isolates the discharge space discharge voltages when only the rib pitch was from the influence of the barrier ribs, but also re- changed while the dimensions of the front plate duces the discharge space. The thickness of the (including the discharge gap, display electrode ion sheath is determined by the electron density and electron temperature in the discharge space, and these values vary over time and position with- 300 Vfn 250 Vf1 200 Vsmn 150 Vsm1 Voltage (V) 100 Margin 50 (× 150) (× 150) (a) 42-inch panel (b) High-resolution panel 0 µ 00.1 0.2 0.3 0.4 0.5 0.6 Height : 150 m Height : 100 µm µ Width : 80 m Width : 45 µm µ Rib pitch (mm) Pitch : 360 m Pitch : 130 µm Figure 2 Figure 3 Comparison of rib shapes.