Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2001-06-07
2004-03-16
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S491000, C349S032000
Reexamination Certificate
active
06707250
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas discharge display device, a plasma addressed liquid crystal display device, and a method for producing the same, and more particularly to a gas discharge display device and a plasma addressed liquid crystal display device having a particular discharge electrode, and a method for producing the same.
2. Description of the Background Art
Plasma addressed liquid crystal display devices (PALCs) have been developed aiming to realize large-sized thin flat displays. A PALC is a liquid crystal display device having a structure in which a liquid crystal cell and a plasma cell are layered together via a dielectric layer therebetween, in which picture elements are switched by using plasma channels. A PALC can be made in a large size and produced at a low cost as compared to a liquid crystal display device using TFTs (Thin Film Transistors).
A plasma cell includes a plasma cell substrate and a dielectric layer, with a plurality of partition walls being arranged therebetween in a stripe pattern. Note that the dielectric layer also functions as a part of the liquid crystal cell. A plasma channel is defined as a space sealed by adjacent partition walls, the plasma cell substrate and the dielectric layer, and the plasma channel is filled with a discharge gas capable of being ionized through discharge. Each of the plasma channels has discharge electrodes (an anode and a cathode) formed on the plasma cell substrate, and the discharge gas is ionized into a plasma state by applying a voltage to the discharge electrodes. This phenomenon is called “plasma discharge”.
A liquid crystal cell includes a liquid crystal cell substrate and the dielectric layer, with a liquid crystal layer being interposed therebetween. On the liquid crystal layer side of the liquid crystal cell substrate, a plurality of signal electrodes in a parallel stripe pattern are formed so as to cross the plasma channels. Moreover, the liquid crystal cell substrate includes, on the liquid crystal layer side, colored layers provided so as to correspond to the signal electrodes. The colored layers are typically red, green and blue layers.
In a PALC, each region at an intersection between a signal electrode and a plasma channel defines a picture element region. The liquid crystal layer in each picture element region changes its orientation according to the voltage applied between the signal electrode and the plasma channel, whereby the amount of light passing through the picture element region changes. An image signal is applied through the liquid crystal layer in each of the picture element regions arranged in a matrix pattern, so as to control the amount of light passing through the picture element region, thereby displaying an image. In the present specification, the minimum unit of display is referred to as a “picture element”, and each region of the liquid crystal display device corresponding to a “picture element” is referred to as a “picture element region”.
A PALC operates as follows, for example, with the plasma channel being the row scanning unit and the signal electrode being the column driving unit.
A line sequential scanning operation is performed by successively and selectively turning the plasma channels into a plasma state by rows. In synchronism with this, a driving voltage is applied to each of the signal electrodes forming the column driving unit. Since a plasma channel selectively turned into a plasma state is filled with an ionized discharge gas, the potential of the plasma channel turned into a plasma state, except for the vicinity of the cathode, is substantially equal to the potential of the anode. Therefore, an amount of charge according to the difference between the potential of the plasma channel and the potential of the driving voltage is induced/stored in the bottom surface of the dielectric layer (the surface on the plasma channel side; hereinafter referred to as the “dielectric layer bottom surface”) located between the plasma channel turned into a plasma state and the signal electrode opposing the plasma channel. At this time, the liquid crystal layer in the picture element region defined by a region where the plasma channel turned into a plasma state and the signal electrode to which the driving voltage is applied intersect each other changes its orientation according to a voltage obtained by capacitance division of the voltage applied to the plasma channel and the signal electrode between the dielectric layer and the liquid crystal layer.
Then, when the plasma channel is de-selected (when the plasma discharge is stopped), the inside of the plasma channel is insulated, and the state where the charge is stored in the dielectric layer bottom surface is maintained until the plasma channel is selected again to be turned into a plasma state. In other words, the potential difference (voltage) between the dielectric layer bottom surface and the signal electrode is sampled and held by the capacitance formed by the dielectric layer bottom surface, the dielectric layer, the liquid crystal layer and the signal electrode. As a result, while the inside of the plasma channel is insulated, the orientation of the liquid crystal layer in the picture element region is maintained by the sampled and held voltage.
As described above, the plasma channel functions as a switching element for controlling the electrical connection/disconnection between the dielectric layer bottom surface and the anode. Moreover, the dielectric layer bottom surface also functions as a virtual electrode. Of course, the rows and columns may be reversed, in which case the anode of the plasma channel is used as the driving unit by applying a driving voltage thereto, and the signal electrode is used as the scanning unit by applying a scanning voltage thereto.
The plasma discharge occurring in a plasma channel is initiated as follows. When a voltage is applied between an anode and a cathode, electrons emitted from the cathode are accelerated by an electric field between the anode and the cathode to collide with molecules of the discharge gas filled in the plasma channel while traveling toward the anode. As a result, the molecules of the discharge gas are excited or ionized to produce excited atoms, cations and electrons. The cations produced by ionization travel toward the cathode, and some of the cations collide with the cathode to produce secondary electrons. A plasma discharge is initiated by the synergistic effect of the ionization of the discharge gas by the electrons and the discharge of the secondary electrons by the cations. Note that the surface of the cathode contributing to the secondary electron emission will be referred to as a “cathode layer”, and the rest of the cathode excluding the “cathode layer” will be referred to as a “lower cathode layer”.
While nickel is often used in the prior art as a material of the cathode layer, nickel is easily sputtered during a plasma discharge due to a high sputtering rate (the number of atoms sprung out of the cathode material when a single ion of the discharge gas collides therewith) of nickel, thereby causing the following two problems. One is the sputtered nickel atoms being attached to the plasma cell substrate and/or the dielectric layer bottom surface, thereby reducing the transmittance, and the other is the conductive nickel atoms being attached to the dielectric layer bottom surface along the cathode layer extending in parallel to the direction in which the plasma channels extend, thereby causing a phenomenon called “busbar phenomenon”.
The busbar phenomenon will now be described. For example, a case where a color display is produced by using three contiguous picture element regions (respectively corresponding to red (R), green (G) and blue (B)) along a single plasma channel will be described. When only the center, green picture element region is turned ON (bright state), a predetermined amount of charge is induced in a region of the dielectric layer bottom surface corresponding to the green picture ele
Hayashi Masatake
Kanno Yoshihiro
Komatsu Hirohito
Morita Yoichi
Okano Kiyoshi
Guharay Karabi
Nixon & Vanderhye P.C.
Patel Ashok
Sharp Kabushiki Kaisha
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