Plasma addressed liquid crystal display with etched glass spacers

• Main Authors: Khan, Babar A, Van Helleputte, Henri R. J. R, Burgmans, Adrianus L. J, Kuijk, Karel Elbert, Bongaerts, Petrus F. G, Bruinink, Jacob
• Format: Patent
• Language: English
• Published: 11.02.2003

This invention relates to plasma channels, to display devices comprising plasma channels, and to plasma-addressed liquid crystal display panels commonly referred to as "PALC" display devices using such channels. PALC devices comprise, typically, a sandwich of: a first substrate having deposited on it parallel transparent column electrodes, commonly referred to as "ITO" columns or electrodes since indium-tin oxides are typically used, on which is deposited a color filter layer; a second substrate comprising parallel sealed plasma channels corresponding to -rows of the display crossing all of the ITO columns and each of which is filled with a low pressure ionizable gas, such as helium, neon and/or argon, and containing spaced cathode and anode electrodes along the channel for ionizing the gas to create a plasma, which channels are closed off by a thin -transparent dielectric sheet; and a liquid crystal (LC) material located between the substrates. The structure behaves like an active matrix liquid crystal display in which the thin film transistor switches at each pixel are replaced by a plasma channel acting as a row switch and capable of selectively addressing a row of LC pixel elements. In operation, successive lines of data signals representing an image to be displayed are sampled at column positions and the sampled data voltages are respectively applied to the ITO columns. All but one of the row plasma channels are in the de-ionized or non-conducting state. The plasma of the one ionized selected channel is conducting and, in effect, establishes a reference potential on the adjacent side of a row of pixels of the LC layer, causing each LC pixel to charge up to the applied column potential of the data signal. The ionized channel is turned off, isolating the LC pixel charge and storing the data voltage for a frame period. When the next row of data appears on the ITO columns, only the succeeding plasma channel row is ionized to store the data voltages in the succeeding row of LC pixels, and so on. As is well known, the attenuation of the backlight or incident light to each LC pixel is a function of the stored voltage across the pixel. A more detailed description is unnecessary because the construction, fabrication, and operation of such PALC devices have been described in detail in the following U.S. patents and publication, the contents of which are hereby incorporated by reference: U.S. Pat. Nos. 4,896,149; 5,077,553; 5,272,472; 5,276,384; and Buzak et al., "A 16-Inch Full Color Plasma Addressed Liquid Crystal Display", Digest of Tech. Papers, 1993 SID Int. Symp., Soc. for Info. Displ. pp. 883-886. A flat display device, preferably of the PALC type, in which the plasma channels are formed by etching laterally-spaced slots in a spacer plate, attaching a thin dielectric sheet over the etched spacer plate, and bonding the etched spacer plate to a transparent substrate such that each channel is formed by the portion of the substrate between flanking walls formed by the etched slots in the spacer plate, adjacent flanking walls in the spacer plate, and the overlying portion of the thin dielectric sheet. By positioning the flanking walls between channel electrode pairs, thus providing glass-to-glass interfaces, anodic bonding can be employed to assemble the three channel elements. Etching can be simplified by pre-attaching the unetched channel plate to the substrate or thin dielectric cover sheet with an intervening etch stop, and etching in situ using the-etch stop to prevent etching of the substrate or thin dielectric cover sheet. In a modification, the thin dielectric cover sheet as a separate element is substituted by depositing a continuous layer or multi-layers including an etch stop on the unetched spacer plate so that, following the etching, the deposited layer or multi-layer remains as the thin channel cover.